how do you stop a bar stud from unscrewing ?

my son was being helpful and cleaned up my yard while I was away. Unfornately he knows nothing about tools. When I went to use my chainsaw, three things were wrong with my craftsman 358357181 model saw. Two of the problems I have resolved and I think I know wat to do here but I'm not sure so before I go ahead I will ask. Somehow he unscrewed the bar stud, the threads aren't stripped and its not broken just came out of the crank case. I screw it in and put the bar and chain on and run it for a few minutes and it loosens again Should I use Locite on the threads of the screw or run a ring of glue around the top or something else?