On second thought my idea to put two males in a tank alone is not a good idea at all. I just sat and watched the tank and I am pretty certain, based on activity, that I have 4 males and POSSIBLY one female. I say possibly because she is the only one now with no signs of nipping.
My LFS is great so I was able to take 3 of the known males and just turn them back in. So I am left with what I am 80ish% certain a male and female in the tank.
The one I think is female now though does still chase what I think is male around but only very little. I changed the caves around so there are two networks, one at each end of the tank. The chasing happens in what looks like cave fight.
I am happy to announce that neither of the two I have are chilling at the top of the tank now.
So what I need now is 3-4 more female yellow labs. I figure all I can do, because I don't want to pay $40+ bucks for mature yellow labs, is go to my LFS and watch the tank for 25 or so minutes and make a best guess which is male and which is female?
If anyone has any advice about sex determination I am all fins! : )