Thieves...
 

I was Superintendent for our local Parks department in the early/mid 80's when scrap prices went through the roof and we had the same issue. We installed steel clips to attach the aluminum slats to the bleacher frame and welded the nuts to the bolt.

This slowed the thieves down, but did not stop them completely.

After a couple of the thieves got nabbed by scrap dealers turning them in..........and the price of aluminum settled down...........it stopped. We still lost thousands of dollars in having to replace the stolen seats.

Joel