The only time I've had Ti stakes bend is if I try to hammer them through a rock (no stake will hold up to that!) or push them in by standing on them. Nearly always, if the stake won't go in, it's because it has hit a rock or a root, and nothing you do will get it in any farther.

You just have to keep moving the stake around until it goes in. If it doesn't, that's when you find a nice big rock to put on the guyline directly in front of the stake.