the best thing you could do for doing quats is to do them in a squat rack....even with somebody spoting you....that way, if you spotter doesn't catch the weight, you still have something there to catch it. I even do use those with light weight. As far as dealifts go....it's all in the from....I've seen guys do it stiff leg and do it fine....and I've seen guys do it with all legs and slip a disk....either way, you gotta be carefull and always wear the right kinda gear(I mean like a weight belt, knee raps, etc....)