Ah, pools and rules
Blargh. I could rant.

If you can't find a diving group which will share their pool time with you, nor a hotel pool (aren't those really shallow?), maybe you can try using your tail without a fin.

I know it sucks, especially if you have a heavier tail, but once they've grown used to you swimming with a tail, you can one day simply leave the fin in, and no one's going to be the wiser.