Don't bother to patch it. The weak points are the small sections of muffler tube that extends from the mufflers. Usually the connection on the passenger side going into the muffler is where it will break. Just get $88 cat-back system and be done with. If you see any rust at any of the joints beware. It may break right there. The pipe to the cat converter is held with a clamp, not welded. But by now it may be fused to the converter and you will have to carefully use a chisel and maybe a saw to cut it/ section it and then remove it without destroying the converter.