Don't laugh, I got this from my grandpa, but...

We used to put mayo on our pointer bitche's biscuits when they were in heat and we hunted them with male dogs. Seemed to work, they'll lick it off after a while and you have to re-apply it.

But when my labs were in season I just kept a close eye on them. You aren't usually working a lab with several other dogs as you would a pointer.