RE: Alternative to Dips?
Legs behind? You'd have to have an odd physique if that makes your torso more horizontal. Have you tried crossing your ankles and bringing your knees up slightly towards your chest, like a bent kneed pike dive. I find this forces my body to stay more horizontal.
Maybe you need to build your shoulder strength up before you're able to do dips with good form. If so, DB or BB bench will help until you have the required strength.