Our gates are all padlocked but that's it. We don't close our stall doors ever, they have runs attached so no way to padlock those.
We used large chains on the gates (wrapped them 'round and 'round before padlocking) so if you cut the lock, you're going to make one heck of a racket, removing the chain. Most of our perimeter fencing is metal panels so you can't cut through it quietly. We don't oil the gates to the corrals so they all SQUEAK.
We've had attempted horse stealings in our area, so it's a concern. Right now though I'm not too worried. My horse has decided that if you see someone with a halter you gallop madly around them for 5 minutes, squealing. Then you come to a screeching halt, walk over and shove your nose in the halter. So I'm sure we'd hear if anyone tried to take her. I can't imagine anyone would *want* our resident Pasture Ornament, she means the world to us but at 26 with arthritis that is obvious, she's not exactly prime "lets steal *that* horse" but she would very quietly leave or load into a trailer.