My pet and I use a pair of real police issue handcuffs when we play. They are double locking so that they will not tighten on her. For safeties sake the key is always attached to them. If our play is going to be particularly rough I will wrap her wrists in a layer or two of leather first for some padding. I also refrain from cuffing her hands behind her back because i want her to be able to easily unlock them if something heavy falls on me, or I pass out from the pleasure she gives me.