My bichon frise- who is 9 years old was just put on prozac... he is not urinating frequently... should I be concerned

You should definitely consult your vet about this! Good luck!
For what reasons did the vet put him on prozac?

Is he drinking regularly that you know of?

Doggie prozak is known to make dogs thirsty.. If he isn't drinking regularly, then you're going to have to go back and get his dosage adjusted.

LJ.. Dogs are typically put on prozak if they are suffering from severe anxiety.

If he isn't drinking enough you can try putting some chicken stock in the water, not the pre packaged stuff, but home made. Also if you can dilute Gatorade or poweraide then that will insure he doesn't become dehydrated.

Lucky already mentioned it, but the prozak or any other anti anxiety will make your pooch extra thirsty.