we bought a "hogtie kit" from the local adult toy store. It has 4 cuffs that velcro closed, with snaps, and d rings. And it had a D ring with snaps to connect them to. (we don't use it much, the resulting hog tie is entirely too loose) I have yet to pull the velcro off just by struggling, and when tied stretched out, I can't reach the clips or the velcro. But they're comfy, strong, and most importantly safe because one grap and pull lets him release me in a hurry (our families choose the most inopportune moments to knock on the door)

good luck finding some you like!