diff --git a/watchdog.go b/watchdog.go
index d3da178..ed26ad7 100644
--- a/watchdog.go
+++ b/watchdog.go
@@ -16,17 +16,57 @@ var (
 // Watchdog keeps checks to run either periodically
 // or on demand.
 type Watchdog struct {
-	checks []*wdCheck
+	checks checksMap
 	mu     sync.Mutex
 
-	monitoring bool // is monitoring currently in progress
-
 	events  chan CheckResult // output channel
 	limiter chan struct{}    // TODO: use proper limiter here
 
-	timeout time.Duration
+	timeout time.Duration // timeout for checks to complete
 
-	running int
+	monitoring bool // is monitoring currently in progress
+	running    int  // number of active checks monitored
+}
+
+type checksMap struct {
+	m map[string]*wdCheck
+}
+
+func (c *checksMap) build() {
+	if c.m == nil {
+		c.m = make(map[string]*wdCheck)
+	}
+}
+
+func (c *checksMap) Map() map[string]*wdCheck {
+	c.build()
+
+	return c.m
+}
+
+func (c *checksMap) Set(key string, v *wdCheck) {
+	c.build()
+
+	c.m[key] = v
+}
+
+func (c *checksMap) Lookup(key string) (*wdCheck, bool) {
+	c.build()
+
+	v, ok := c.m[key]
+	return v, ok
+}
+
+func (c *checksMap) Delete(key string) {
+	c.build()
+
+	delete(c.m, key)
+}
+
+func (c *checksMap) Len() int {
+	c.build()
+
+	return len(c.m)
 }
 
 type wdCheck struct {
@@ -37,29 +77,23 @@ type wdCheck struct {
 // New creates instance of Watchdog with
 // provided checks.
 func New(checks ...Check) *Watchdog {
-	ch := make([]*wdCheck, len(checks))
-
-	for i := range checks {
-		ch[i] = &wdCheck{
-			check: checks[i],
+	w := Watchdog{}
+	for _, c := range checks {
+		nc := &wdCheck{
+			check: c,
 		}
+
+		w.checks.Set(c.Name, nc)
 	}
 
-	w := &Watchdog{
-		checks: ch,
-	}
-
-	return w
+	return &w
 }
 
 func (w *Watchdog) ListChecks() []Check {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 
-	out := make([]Check, len(w.checks))
-	for i := range w.checks {
-		out[i] = w.checks[i].check
-	}
+	out := w.copyChecks()
 
 	return out
 }
@@ -81,20 +115,27 @@ func (w *Watchdog) SetTimeout(d time.Duration) {
 // AddChecks adds checks to the group.
 // If monitoring is in progress then monitoring it started for the newly added
 // check as well.
-// Check may have duplicate Name fields but note that RemoveChecks removes checks
-// by their Name fields.
+// Check may have not have duplicate Name fields. New check with the same
+// hame overwrites the previous one.
 func (w *Watchdog) AddChecks(checks ...Check) {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 
-	for i := range checks {
+	for _, c := range checks {
 		nc := &wdCheck{
-			check: checks[i],
+			check: c,
 		}
-		w.checks = append(w.checks, nc)
+
+		old, haveOld := w.checks.Lookup(c.Name)
+
+		w.checks.Set(c.Name, nc)
 
 		if w.monitoring {
 			w.startMonitoring(nc)
+
+			if haveOld {
+				w.stopMonitoring(old)
+			}
 		}
 	}
 }
@@ -104,19 +145,18 @@ func (w *Watchdog) RemoveChecks(names ...string) {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 
-	remaining := make([]*wdCheck, 0, len(w.checks)-len(names))
-	for _, c := range w.checks {
-		if slices.Contains(names, c.check.Name) {
-			if w.monitoring {
-				w.stopMonitoring(c)
-			}
+	for _, name := range names {
+		c, ok := w.checks.Lookup(name)
+		if !ok {
 			continue
 		}
 
-		remaining = append(remaining, c)
-	}
+		if w.monitoring {
+			w.stopMonitoring(c)
+		}
 
-	w.checks = remaining
+		w.checks.Delete(name)
+	}
 }
 
 // Start starts monitoring.
@@ -132,7 +172,7 @@ func (w *Watchdog) Start(concurrency int) (<-chan CheckResult, error) {
 	w.mu.Lock()
 	defer w.mu.Unlock()
 
-	if len(w.checks) == 0 {
+	if w.checks.Len() == 0 {
 		return nil, ErrNotConfigured
 	}
 
@@ -141,7 +181,7 @@ func (w *Watchdog) Start(concurrency int) (<-chan CheckResult, error) {
 	}
 
 	if concurrency == 0 {
-		concurrency = len(w.checks)
+		concurrency = w.checks.Len()
 	}
 
 	if w.timeout == 0 {
@@ -151,12 +191,10 @@ func (w *Watchdog) Start(concurrency int) (<-chan CheckResult, error) {
 	w.events = make(chan CheckResult, concurrency)
 	w.limiter = make(chan struct{}, concurrency)
 
-	for i := range w.checks {
-		w.startMonitoring(w.checks[i])
+	for _, c := range w.checks.Map() {
+		w.startMonitoring(c)
 	}
 
-	w.monitoring = true
-
 	return w.events, nil
 }
 
@@ -170,8 +208,8 @@ func (w *Watchdog) Stop() error {
 		return ErrNotRunning
 	}
 
-	for i := range w.checks {
-		w.stopMonitoring(w.checks[i])
+	for _, c := range w.checks.Map() {
+		w.stopMonitoring(c)
 	}
 
 	return nil
@@ -182,7 +220,8 @@ func (w *Watchdog) Stop() error {
 // Otherwise at most concurrency checks will be allowed to run simultaneously.
 func (w *Watchdog) RunImmediately(ctx context.Context, concurrency int) ([]CheckResult, error) {
 	w.mu.Lock()
-	if len(w.checks) == 0 {
+
+	if w.checks.Len() == 0 {
 		w.mu.Unlock()
 		return nil, ErrNotConfigured
 	}
@@ -209,41 +248,28 @@ func (w *Watchdog) RunImmediately(ctx context.Context, concurrency int) ([]Check
 }
 
 func (w *Watchdog) copyChecks() []Check {
-	cp := make([]Check, len(w.checks))
-	for i := range w.checks {
-		cp[i] = w.checks[i].check
+	cp := make([]Check, 0, w.checks.Len())
+	for _, v := range w.checks.Map() {
+		cp = append(cp, v.check)
 	}
 
 	return cp
 }
 
 func (w *Watchdog) startMonitoring(wdc *wdCheck) {
-
 	wdc.stop = make(chan struct{})
 	c := wdc.check
 
-	// this method is called only with
-	// w.mu locked
+	if !w.monitoring {
+		w.monitoring = true
+	}
+
 	w.running++
 
 	go func() {
-		defer func() {
-			w.mu.Lock()
-			defer w.mu.Unlock()
-
-			w.running--
-			if w.running == 0 {
-				// last goroutine to exit will also
-				// close the output chan
-				close(w.events)
-				w.monitoring = false
-			}
-		}()
-
 		state := CheckResult{
-			// if first run return anything
-			// other that OK, we'll report it
-			// if first run is OK, then we do not need to report
+			// on first run return anything
+			// other that OK
 			Status: StatusOK,
 		}
 
@@ -259,17 +285,19 @@ func (w *Watchdog) startMonitoring(wdc *wdCheck) {
 
 			<-w.limiter
 
-			s := CheckResult{
+			r := CheckResult{
 				Name:   c.Name,
 				Status: status,
 				Error:  err,
 			}
 
-			if s.Status != state.Status || s.Error != nil {
-				w.events <- s
+			// if status changed or we've got an error
+			// then report this
+			if r.Status != state.Status || r.Error != nil {
+				w.events <- r
 			}
 
-			state = s
+			state = r
 
 			select {
 			case <-ticker:
@@ -284,23 +312,26 @@ func (w *Watchdog) startMonitoring(wdc *wdCheck) {
 
 func (w *Watchdog) stopMonitoring(wdc *wdCheck) {
 	close(wdc.stop)
+	w.running--
+
+	if w.running == 0 {
+		w.monitoring = false
+		close(w.events)
+	}
 }
 
 func runChecksConcurrently(ctx context.Context, ch []Check, concurrency int) []CheckResult {
-	statuses := make([]CheckResult, 0, len(ch))
-	m := sync.Mutex{} // for append operations
-
 	sema := make(chan struct{}, concurrency) // semaphore to limit concurrency
-	done := make(chan struct{}, len(ch))
-
-	count := len(ch)
+	done := make(chan CheckResult, len(ch))
 
+	wg := new(sync.WaitGroup)
+	wg.Add(len(ch))
 	for _, e := range ch {
-		sema <- struct{}{} // acquire
-		go func() error {
+		go func() {
+			sema <- struct{}{} // acquire
 			defer func() {
-				<-sema
-				done <- struct{}{}
+				<-sema // release
+				wg.Done()
 			}()
 
 			// relying on assumption that CheckFunc obeys context
@@ -313,21 +344,21 @@ func runChecksConcurrently(ctx context.Context, ch []Check, concurrency int) []C
 				Error:  err,
 			}
 
-			m.Lock()
-			defer m.Unlock()
-			statuses = append(statuses, r)
-
-			return nil
+			done <- r
 		}()
 	}
 
-	// wait for all to finish
-	for range done {
-		count--
-		if count == 0 {
-			close(done)
-		}
+	go func() {
+		wg.Wait()
+		close(done)
+	}()
+
+	results := make([]CheckResult, 0, len(ch))
+
+	// collect results
+	for r := range done {
+		results = append(results, r)
 	}
 
-	return statuses
+	return results
 }