Great footage. I am very envious of all his smoothly-moving bolts! It'd take more than a young stirk's tongue to shift some of ours...
We have similar gates, with just one bolt, and years ago BH had a very similar experience to this farmer - but wasn't able to video it so could never prove it to anyone else. He then adapted the gates to put a piece of metal on the top which has to flop over and lock into the H girder the gates are mounted on.
This winter I had a similar experience, and at first I thought I must have left the flop-over back, so made doubly sure - turned out one of our Blue-greys (in for a few days for calving when the weather was evil) had accidentally discovered about the flop-over by rubbing her neck very vigorously - and the thing about cows is, they learn really quickly.
My Fell gelding thankfully lacks quite the brains of Daphne the Blue-grey; I see him watching me closely when I'm opening gates from his back, but they have to be extremely simple for him to be able to do it himself. When I finally get riding my young mare I think it may be a different story...