(Below) Here's a simple fix. The issue is that the rubber mounts surrounding the two studs which protrude through the fender have shrunk with age. I give them a new lease on life by simply inserting two internal tooth lock washers onto the studs (external tooth would also work).
Those teeth will grab the fender and hold everything tight.
Pop them into place to complete our tail tidying chores.
Here's an Amazon link.