diff --git a/lib/simply_based/redis.rb b/lib/simply_based/redis.rb
index 5b5b221..e93fea8 100644
--- a/lib/simply_based/redis.rb
+++ b/lib/simply_based/redis.rb
@@ -7,12 +7,15 @@ module SimplyBased
   # All three use the same cluster/bucket as your models — one datastore.
 
   # Server-side atomic counters (Couchbase binary increment/decrement). A drop-in
-  # for Redis INCR/DECR.
+  # for Redis INCR/INCRBY.
   #
   #   counter = SimplyBased::Counter.new
-  #   counter.increment("jobs:processed")       # => 1 (created at 0, +1)
+  #   counter.increment("jobs:processed")       # => 1 (like Redis INCR on a missing key)
   #   counter.increment("jobs:processed", 5)     # => 6
   #   counter.get("jobs:processed")              # => 6
+  #
+  # Divergence from Redis: Couchbase counters are unsigned 64-bit —
+  # decrementing below zero clamps at 0 (Redis DECR would go negative).
   class Counter
     def initialize(store: nil)
       @store = store
@@ -22,10 +25,16 @@ module SimplyBased
       @store ||= SimplyBased.database
     end
 
-    def increment(key, by = 1, initial: 0, ttl: nil)
-      store.counter_incr(key, by, initial: initial, ttl: ttl)
+    # Matches Redis INCRBY semantics: incrementing a missing key seeds it at
+    # `by` (Couchbase's native increment would seed at `initial` and *ignore*
+    # the delta on creation — the first INCR would return 0, silently
+    # undercounting). Pass an explicit `initial:` to override.
+    def increment(key, by = 1, initial: nil, ttl: nil)
+      store.counter_incr(key, by, initial: initial || by, ttl: ttl)
     end
 
+    # A missing key seeds at `initial` (default 0): Couchbase counters cannot
+    # go negative, so Redis DECRBY parity (-by) is impossible here.
     def decrement(key, by = 1, initial: 0, ttl: nil)
       store.counter_decr(key, by, initial: initial, ttl: ttl)
     end
@@ -101,15 +110,28 @@ module SimplyBased
     end
 
     # Returns a CAS token (the lock handle) or nil if already held.
+    # A positive ttl is mandatory: without expiry, a crashed holder would leave
+    # the lock stuck forever.
     def acquire(key, ttl: 30)
+      raise ArgumentError, "lock ttl must be a positive number of seconds (got #{ttl.inspect})" unless ttl.respond_to?(:positive?) && ttl.positive?
       store.kv_add(lock_key(key), { 'locked_at' => Time.now.to_i }, ttl: ttl)
     end
 
-    # Release only if we still hold the same CAS (no stomping a re-acquired lock).
-    def release(key, cas = nil)
+    # Release only if we still hold the same CAS (no stomping a lock that
+    # expired and was re-acquired by someone else). The handle is required —
+    # a nil CAS used to delete the lock document unconditionally, letting any
+    # caller unlock a lock it never held. Returns false when the handle is
+    # stale (someone else holds the lock now).
+    def release(key, cas)
+      raise ArgumentError, 'release requires the CAS handle returned by acquire (use force_release! to override)' if cas.nil?
       store.kv_delete(lock_key(key), cas: cas)
     end
 
+    # Unconditional unlock — administrative override only.
+    def force_release!(key)
+      store.kv_delete(lock_key(key))
+    end
+
     def with_lock(key, ttl: 30, retries: 0, wait: 0.1)
       cas = acquire(key, ttl: ttl)
       tries = 0
diff --git a/spec/redis_replacements_spec.rb b/spec/redis_replacements_spec.rb
index 38f8714..d338d2c 100644
--- a/spec/redis_replacements_spec.rb
+++ b/spec/redis_replacements_spec.rb
@@ -6,11 +6,16 @@ RSpec.describe 'Redis replacements' do
   describe SimplyBased::Counter do
     subject(:counter) { described_class.new }
 
-    it 'atomically increments, seeding at the initial value' do
-      expect(counter.increment('c:hits')).to eq(0)        # created at initial 0
+    it 'atomically increments with Redis INCR semantics (first INCR of a missing key returns the delta)' do
       expect(counter.increment('c:hits')).to eq(1)
-      expect(counter.increment('c:hits', 5)).to eq(6)
-      expect(counter.get('c:hits')).to eq(6)
+      expect(counter.increment('c:hits')).to eq(2)
+      expect(counter.increment('c:hits', 5)).to eq(7)
+      expect(counter.get('c:hits')).to eq(7)
+    end
+
+    it 'seeds at an explicit initial value when given' do
+      expect(counter.increment('c:seeded', 1, initial: 100)).to eq(100)
+      expect(counter.increment('c:seeded')).to eq(101)
     end
 
     it 'decrements and resets' do
@@ -19,6 +24,11 @@ RSpec.describe 'Redis replacements' do
       expect(counter.reset('c:n', 0)).to eq(0)
       expect(counter.get('c:n')).to eq(0)
     end
+
+    it 'clamps decrement at zero (unsigned Couchbase counters; Redis would go negative)' do
+      counter.reset('c:clamp', 1)
+      expect(counter.decrement('c:clamp', 5)).to eq(0)
+    end
   end
 
   describe SimplyBased::Cache do
@@ -45,6 +55,19 @@ RSpec.describe 'Redis replacements' do
       expect(lock.acquire('job:1', ttl: 30)).not_to be_nil # released → free
     end
 
+    it 'refuses to release without the CAS handle' do
+      lock.acquire('job:guard', ttl: 30)
+      expect { lock.release('job:guard', nil) }.to raise_error(ArgumentError)
+      expect(lock.acquire('job:guard', ttl: 30)).to be_nil # still held
+      lock.force_release!('job:guard')
+      expect(lock.acquire('job:guard', ttl: 30)).not_to be_nil
+    end
+
+    it 'rejects a missing/zero ttl (a crashed holder must never leave an immortal lock)' do
+      expect { lock.acquire('job:immortal', ttl: nil) }.to raise_error(ArgumentError)
+      expect { lock.acquire('job:immortal', ttl: 0) }.to raise_error(ArgumentError)
+    end
+
     it 'runs a critical section with with_lock' do
       ran = false
       lock.with_lock('job:2') { ran = true }