The trick "play dead"

I would love to teach Keeper and Toupe the trick "play dead". Does anyone have any training tips on how to teach them? Thank you :D

when I tought Misty to play dead, I said "bang" and rolled her over, as soon as she was in her back and gave her a treat, then I would let her up again, say "bang" and roll her over and treat only took 2-3 times before she rolled over on her own when I said "bang" but some people will tell you to roll the dog over and then say bang, however that does'nt work with my dogs lol