The 3M adhesive isn't a 100% solution and you already proven that by being able to knock off both OEM covers, presumably with foot dragging action. 3M is likely a better solution but you'll still have to be more careful with your foot. I had a similar problem--knee-- and was able to make things better with the adhesive and not dragging against the pedal.
What I do is remove the old pad and get off as much old glue off the metal as I can. Then I spray coat both the metal and pad as instructions instruct. I try to do this on a hot day so the rubber is more flexible.
After the glue has "tacked" I put the pedal on, make sure the under edges are correctly wrapped around the metal and then squeeze the pad on the pedal and form fit it. I leave the tractor in the hot sun for a while and don't use the tractor for a day or so. Then I use it and be careful and after a small learning curve have not had any pedal pads come off.
I did stop/slow dragging my foot, however since I don't think any glue would hold against foot dragging over the. edge on a regular basis. I suppose you could epoxy the pedal pad on but would never get the pad or epoxy off again. Good luck and update if you can.