I use a bivy bag and a tarp.

I've considered a hammock many times but unless you can tie them up to something, they're dead weight.

I'm with BigDaddyTX when it comes to ill intentioned people and critters...they don't care if you're in a tent or not and if you're sleeping you won't either until you wake up. Unless you're sleeping fully clothed and equipped without a sleeping bag or anything, you wouldn't be in a position to move very quickly even if you did wake up first.

Either way you take your chances.