It's too late to talk about untying a knot, so let me just comment that there is a knot for every application, and there is a knot available for every load that can be untied.
The alpine butterfly is highly recommended for mid-line knots, but it will sure bind up tight. Double bowline...probably ok.
I usually pipe up at times like this with my favorite midline knot : Man-harness knot. It always unties, but it is not without it's imperfections, too.
If you are ruining ropes with knots that don't come out, then you need to spend a little more time each evening studying the books, and practicing the ones you don't know too well. Eventually, you won't be posting questions.
BTW: there is a special knot that is purpose built for towing trucks out of the mud, Jeff. I forget the name, but it is listed in ABOK, and I have used it very effectively. If you want, I can post a picture.
