No, that is not how it works. Criminals never go on a joyride to see if they can find livestock to steal there and then. They do their homework before the time to see where an easy spot is to herd livestock, force them into a corner to catch and load them close to a road to aid loading. In order to do this they visit the area before the time on a casual drive by to scout and see. If they cannot enter the property they cannot see. If they break a lock to scout you know unwanted people were there, they know you know too and that you will probably be alert.
Livestock thieves dont drive around and pick up livestock. It is simply not that easy. After the scout, 2 or 3 have to be dropped off at or close to the identified spot, where they then herd the sheep to that spot. Once they are there with the sheep, the vehicle comes closer and stops to load.
You dont have to believe it, but to prevent free access does curb theft. Crimials are like water, they go to the easiest spots first and if there is something that makes it difficult for them, they will likely go somewhere else. I am not thumbsucking, I talk about experience.