Loop hole - firing mediators

[NorthernGirl]

DH has a joint guardianship agreement with his UBPDx for their son who is 20 and has special needs. It took months to come up with the agreement, and just getting the agreement signed took a few mediators. UBPDx fires all mediators, counsellors, etc. Given her history, DH insisted that the joint agreement include something about how neither person could dismiss the mediator -- they must both agree.

They used one mediator as a test on a real issue just prior to signing the agreement and when the mediator didn't side with UBPDx, she decided they should find a new mediator. She found another and insisted DH and she meet the mediator in person, and then used the session to attack DH. DH said as he stayed calm, she lost her composure. A few days later she sent DH a note and said the mediator wasn't appropriate. So they had an agreement but she wouldn't agree to any mediator. DH had to get his lawyer involved and letters went back and forth to force his ex to finally find a new mediator. She settled on a retired judge.

They used this mediator/retired judge for the first time a few weeks ago. After one session, she sent a note to the mediator saying she had found out he has some loose connection to DH's lawyer's law firm. The mediator had sold part of his legal practice to one of the lawyers in DH's firm. The mediator sent a note saying he did not know DH's lawyer, had no association with this lawyer, and so therefore could see no reason for bias.

DH's ex then sent an email saying she was pulling out of the mediation. The mediator said he would then move to arbitration. He reviewed all the information sent by DH and by his ex, and agreed with DH. DH's ex then sent a long letter accusing the mediator of being biased for a number of reasons. It was fascinating reading -- considering she was telling a retired judge that he was biased because he was a male. The letter had lots of legal jargon so it was clear that her brother, who is a lawyer, was involved.

The mediator talked to DH and said he understood the agreement saying that neither could dismiss the mediator, but he felt he could not properly do his job if she felt he was biased. So basically DH's ex found the loophole -- insult the mediator so he withdraws.

DH's lawyer says that basically if the mediator doesn't want to try to mediate with someone who is clearly unstable, then it is hard to make the agreement stick. So now what?

If the agreement doesn't stop her from getting rid of mediators, how does this not just keep happening? Any ideas?