A: Except in board meetings and committee meetings, the presiding officer should not participate in the debate. (RONR pp. 389-90.) It is precisely for the situation you describe that this rule exists. If your moderator begins to participate in debating the merits of an issue, you may raise a Point of Order, referring to this rule. (RONR Section 23.) Should the moderator then rule your point not well taken, you may then Appeal from the Decision of the Chair, which puts the question in the hands of the assembly. (RONR Section 24.)

Likewise, when a motion is made that refers to the moderator in a manner not in common with other members (e.g., that commends or censures him), he should turn control of the meeting to a vice-president or some other member. (RONR p. 443.) If he does not, you may move a Point of Order and, if necessary, Appeal.

If your moderator ignores the Point of Order, you may move it again (and it must be seconded each time). If after two attempts, you, yourself, may put the question to the assembly, standing in your place. (RONR pp. 656-7.)

It isn't improper for your moderator to "serve as the parliamentarian." But understand that the parliamentarian's job is not to rule on parliamentary questions; he serves solely as an advisor and has no authority. The moderator (presiding officer) does have the authority and responsibility to rule on parliamentary questions, with the assembly being the final authority (thus the ability to Appeal). Of course this authority is subordinate to the governing documents and all laws and ordinances. (RONR p. 560.)