That said there are only 2 anal poses Kneeling spoons and the anal doggy,… decline to accept them and offer another choice. Be clear that anal is not a turn on but a mood killer,… and as kitten' says play is mutual… don't accept an action if you don't like it. Good men will repsect that. If they don't then I guess they aren't a decent sort are they?
Dominates/Tops around here will typically insist on the option, most likely because they see it as a taboo element missing from their RL experience… that is your choice if you choose to yield. Good Dom's will take it under consideration,… if you establish that as a boundary a Dom will/should respect it. Great Dom's will consider it a challenge… to find a way to lead you to the fulfillment of it's potential enjoyment without breaking the boundaries.
I will say that some women banner “no anal”… reserving it for special partners… you need to be clear ahead of time that it is a mood killer and you don't enjoy it.