I don't really consider any lasers to be "waterproof" more like weather resistant.
If you really want a waterproof laser, wouldn't be that hard to add some o-rings, oil them, and all threads, and so long as you don't change focus, you'll be ok. Only place in the laser that I'm not sure about, is where the lens is mounted... I'm pretty sure the seal there is waterproof too.
Also Lowell is absolutely 100% right, any waterproofing lens on top of the focusing lens, you're losing some power, and more importantly, you will have splash around the dot.