Play isn't a break from training — it's training. The cues you teach during games stick because your pet is having a great time.
Tug, played right
Teach "take it" and "drop it" within the game. Pause every minute or two to ask for a sit before resuming. Tug doesn't cause aggression — uncontrolled tug does.
Fetch as a reset
Two or three throws, then a short obedience break, then more throws. This pattern keeps arousal in check and turns fetch into a training tool.
End every game while your pet still wants more. They'll be eager to play again tomorrow.