When we moved to the farm when I was a kid, I got a dog that would not stay on the property. Every time we had him off his chain and didn't have an eye on him, he'd slip away and wouldn't come back for a day or three. All of the responsibility was on me/us, but he was a sneaky dog too. He came home one time with a .22 round in his hind leg. No way for us to tell where he picked it up. We stepped up our game of keeping him in check, and he didn't much want to wander for the next few months either, so it made our job easy. After he healed up, we'd become lax and he snuck off again. We never saw him again, so my assumption is the farmer was a better shot that time. I figure that he was either going to spend his life in a kennel or on a chain, or wander like he did and meet his ultimate fate at the end of a neighbors gun.
Point being, even a dog with a GPS collar can pick up a chunk of lead at any unknown point in their explorations, and every farmer I know owns a readily available .22 rifle for dispatching pests.