In high-performance applications where a failure can be worth big money, engine builders will often "pin" the freeze plugs to further ensure they won't come out. The process is fairly simple and you can do it yourself. Drill three holes just above the lip of each plug (on the chamfer of the plug bore in the block). Use a No. 38 bit and drill the holes on a 45-degree angle until they are approximately 0.300-inch deep. Now you can tap the holes and use button-head screws or use freeze-plug pins made specifically for this task. These pins save you the effort of having to tap each hole. Just use Loctite on the pins just like you do the plug itself.