As I am doing body work, part of this is removing any bondo that folks have slapped on over the decades. I am using an old trick to do this and thought I'ld share. Perhaps everyone knows this one, but if it helps even one person then it's worth sharing.
Instead of drilling, chopping, hammering, chistling and try to force the bondo off the car do this. Get Aircraft Paint Stripper. Soak and old rag in it. Put that over the bondo and cover with plastic like a plastic grocery bag. Tape it in place. Repeat a few times as you work on other stuff.
The aircraft paint stripper soaks into the bondo and makes it rubbery so you can just peel it off, or use a screw driver on it (it falls off pretty easy). This way you are not smacking up the metal around and under the bondo or spending a ton of time fighting it.