I bought some of those waxy cattle paint markers and coated my buck's undercarriage with it (from just between his front legs to just in front of his important parts), refreshing it every two or three days. When he mounts the does it leaves a smear of blaze orange on their bum. I put an X on the calendar on that day. This is my first year doing it and so far he has only left marks on his wether friend, and that only on his side so clearly from rough-housing not actually breeding attempts. The first year I had goats I never ever saw my does come in to heat, be bred, have discharge, etc. and I was out there looking at them every single day. Every single one of them kidded for me, though, so he got the job done.