eclipse785:Funny, my regular buddy dives with a Zeagle BC (Ranger, I beleive) which has two tank straps. My Dacor BC only has one. While I like his BC better in general, about 1 in every 5 dives his tank slips out (usually just before getting into the water). Mine has never had that problem.
Maybe he has bad technique? The velcro on a Zeagle is amazing. If you can get the strap tight enough, it would hold without a buckle.