No offense to ZT--I own and like them myself--but if you want a "hard use" folder (a concept I kinda' reject, for folding knives, but that's a rabbit trail), you probably don't want ZT and you don't want a frame lock. Like, at all. You want some kind of a super strong back lock. I'd start with something in the Cold Steel line, as somebody already suggested in the thread. Cold Steel Recon is an affordable option. Cold Steel Ultimate Hunter is another, with a strong tip. The SR1 as suggested is a bit more, but even thicker blade stock, and you may want that. The 4Max is a monster, but seriously, if you're gonna get something THAT big, why not just go with a fixed blade.