Erwin Mendelson has resigned as a member of Maryland Racing Commission, saying he was fed up with the rancor and disgusted by the continuing fighting between racing's factions."I've had enough," said Mendelson, who served more than four years on the nine-member panel. "It's no fun; we're going downhill. I don't need the heartache and the aggravation anymore."A certified public account, Mendelson lives in Bethesda and owned a large stable of racehorses in the 1970s and 1980s. He said several events led to his decision to resign.Gov. Robert Ehrlich Jr.'s recent appointment of the newcomer Tom McDonough as commission chairman was a "big mistake," Mendelson said.He said he likes McDonough and thought he would grow into the job. But, Mendelson said, throwing someone with no commission experience into that demanding post was not fair to McDonough, the commission or Maryland racing.And, he said, the recent dispute between horsemen and track management over the threatened closing of the Pimlico Race Course barn area for the winter was a "fiasco." The unruly meetings, the inappropriate public outbursts and the follow-up accusations by the horsemen's association that the commissioners had lied and met in secret were the final straw, Mendelson said.Before voting not to interfere in the dispute, an act that incensed horsemen, commissioners never discussed the issue outside the public meeting, Mendelson said."I didn't need to be chastised by the horsemen like that," he said.Mendelson, whose resignation became effective Dec. 31, said his parting advice is "for the horsemen and the tracks to unite and get together to get a slots bill passed. We need it desperately."Ehrlich has already appointed a replacement for Mendelson. He is Gregory Barnhill, 50, a partner and senior advisor at Brown Investment Advisory & Trust Co. A resident of Stevenson, Barnhill has owned steeplechase horses for 25 years.