I just put a sticky note on the tub of every adult female I have. If a male goes into her tub, I write down which male and if there was a lock. This is also where I eventually write down ovulation and pre-lay shed dates.

At the end of the season, I take the sticky notes down and put everything into my breeding records binder and put photos of the pairings on my computer (especially important if you deal with recessive morphs!).