You must be able to control your dog at all times and aggressive dogs must be immediately removed.
Playful actions to watch for:
Back and forth play – dogs change position – role reversals
Bouncy, exaggerated gestures
Wiggly bodies
Open relaxed mouth
Play-bows
Twisted leaps or jumps
Pawing the air
Signs of Anxiety/Stress to Monitor:
Fast wagging low tail
Whining or whimpering
Ears may be back
Hiding behind objects or people
Signs of Fear:
Dog will try to look small
Tail tucked
Hunched over, head down
Tense
May urinate submissively
Red Flags that Require Intervention:
Excessive mounting
Pinning (holding another dog down and standing stiffly over them)
Shadowing another dog (following) incessantly
Bullying: repeatedly bothering another dog that does not want to interact
Fast non-stop running with a group – high arousal situation
Full-speed body slams
Putting head repeatedly onto another dog’s neck or back
Staring with a fixed gaze directly at another dog
Snarling or raised lips
Showing teeth
Hackles up at the shoulders
*Association of Professional Dog Trainers, apdt.com