I use a soft belt like the ones from Rehband when I hit the 50% mark. When I am at 75% the soft belt comes off and the hard belt goes on. Anything at 90% or when I am going for something like a very heavy yolk run or or where I'll be giving max effort over several reps, the hard belt is on over the top of the soft belt.
B-
Damn bro, two belts? That's hardcore lol