What is the best way to remove a hack job done with bodyfiller ?

I've already taken a lot out of the fender whilst knocking out some of the bad dents, but there is a 1/4 " thick layer all over this one fender . " This stuff is still gummy! " .

I tried heating the back of the fender with a torch, but I don't want to do more damage then good.

any one have a better solution the setting out there with a scraper and grinder ? or buying another fender ?