Determining which units are rental units once restriction is in place

Hi,
I've gone through a search and notice many posts on restricting rental units but I did not find one that addresses how to determine which units are rentals when you are near the limit. For example, we are a small community and rentals are restricted to no more than 5. We now have 2 owners who have indicated that they want to rent their unit and are vying for the 5th space, and both approached the HOA at around the same time. Do any of your HOAs have rules or guidelines for determining which units are rentals?
thanks

We know which units are the rentals. I apologize that my question was not worded cleary. What we are looking for are guidelines for determining which unit should be rented out if more than 5 owners want to rent the unit. DO you do a lottery system and what are the rules governing the lottery? Do you go by seniority? Do you go by credit rating of the prospective tenants? etc. Does this question make sense? I'm not trying to determine which units are rented out. We're trying to come up with fair rules that govern the selection of units as we're approaching the limit.

Mel:

I believe the fair route would be a 1st come 1st serve list. If there are 5 rented now and that is the limit then a waiting list needs to be established.