I've never has a problem with my tripod head coming loose, but I think you are describing a balance between the drag adjustment and the pressure applied to tighten the head.
Is the pan screw tight enough to keep the head from spinning when you tighten it? I've always been able to hand tighten the head, but if the pan screw is not tight, the head just spins. Tighten the pan screw enough to hold the head. You should be able to hand tighten the head onto the tripod.
If you need to use glue you could try a single drop of blue Loctite (not Red Loctite).