i lock with sheldon's method using a krypto new york mini
1. Don't lock to trees. It can harm the trees and ur wallet (as u can get fined). Don't lock to anything that moves, are too thin, or removable. (no fences, scaffolding, mailboxes, street signs without signs, etc)
2. What veganwar said. Old chain to tube to tie down ur saddle. And then I would do Sheldon's lock method with mini u-lock AND cable for front.
3. (see 2)

in case u dont' know what we mean by old chain and tube to saddle, here: