good luck to you! i really feel for you because our mimi would not stop poo pooing in her crate, and she could hold it all night but the moment we left even if only 1 hour--she would poo in her crate! i felt like i was losing my mind. the solution to our problem was to put our other boxer's crate near hers so that they could see each other. she finally stopped after that and that was at five months i think.
dont give up! i told my husband several times that we wouldnt give away our child if he/she kept wetting the bed or having accidents during potty training, so there is no way we would give away our mimi.
since it sounds like you have tried so many things without success, it sounds like an actual physical problem (maybe neurological). maybe this isnt a good comparison, but friends of ours have a daughter who is not completely potty trained at 5 yrs. after so much frustration, they have found out that their daughter doesnt get the sensation to go, so she doesnt realize when she has to go. . .
anyways, hope you can make progress!
love
kk, rocky, and mimi