Pipe cut at the ground? Fill the pipe with concrete. Does anybody really cut the whole pipe anyway?
Bolts cut/broken, chains and basket slipped off the pole? Weld chain assembly and basket to the pole. Alternatively, I've heard of an epoxy(?) caulk-like stuff that is cost-effective, easy to apply, and holds essentially like a weld.
Cement base dug out? Use more cement. Or, more effectively, before putting cement in the hole, drive rebar diagonally into the sides of the hole.
Lock cut? Use more effective locks. None are impervious, but the vending locks we used for years at Gview, Walnut, Southwoods seem to be pretty good. I forget where I ordered them, but they were very cost-effective.
Tab on locking collar cut, pole slipped out of sleeve? First, this is difficult to do, so hopefully it's not much of a problem. The only defense I can think of: Bond (epoxy or weld) the pole to the sleeve (if you never need to take the pole out of the sleeve); or, reinforce the tab itself.
What other methods of theft are there?