Why would you worry about the workers shooting and dragging off a calf? People seldom do that in an area where they could easily be caught? Blood trail right to them?
Cattle are stolen in the more remote areas where they are less likely to get caught. It is done is as fast and quiet a manner as possible... Not where people are in and out, off and on, at different times of the day....
Cattle that get shot and left are usually stupid idiots that get joy out of hurting another animal... joy/thrill seekers...most are done from cars along the road, where they can drive off in a hurry.... and the ones that shoot and gut quickly for the meat aren't going to do it where there are people around most of the time. Working on the house being built next door is probably better for you as they are more than likely to be watching out for you in a way... if they like sitting and eating next to the electric fence, they are more than likely to notice if something is different .
If I remember from your early posts, you are not out in a remote area. Sure, it can happen anywhere, but I think you are causing yourself undue worry.