1970 GTO Endura Bumper Studs Turning....
 

Is there a proper way to secure/fasten the studs on the back side of the endura bumper to stop them from turning?

I removed my headlight brackets and in the process one stud started to spin because of the nut rusting to it. I managed to get my die grinder in there and took one side off the nut and then cut a slit in the tip of the stud so I could use a screwdriver to hold it and fortunately, I got the nut off.

Now...what is the best way to secure this stud so that it doesn't spin again?

Thanks