The rear shock dust tub covers back up I have tried but they keep coming back down, I can see a Stanley knife job here to remove them

Usually the rear bumpstops shove into the dust tubes, then the bumpstops nip in the cups where they meet the body.

My guess is that your bumpstops have perished or become worn and letting the tube slide down.

I wouldn't recommend cutting it off as its what stops the main shocker rod getting covered in dirt.

Theres a bolt at the bottom of the shocker and 2 or 3 at the top although there under the arch liner there pretty easy to get to. Take these out, and it comes out from under the arch pretty easily, its a case of pulling the old bumpstop out and putting the new one in and refitting everything.