Mare Magic is supposed to be good. From what I understand it's more of a natural herbal supplement that helps with hormones. Too bad it wouldn't work on my grumpy gelding,lol.
As mentioned above, some mares are just hussies. My BO used to have a mare that would back up to the light pole in the pasture when in season, after several years the pole actually had to be reset because it was like the leaning tower of Pisa. Some will actually "do the deed" with geldings, especially if they were gelded late and know what to do with their equipment.
My gelding is in with mares, but he is very dominant and unless he's kept with a single mare he doesn't get lovestuck or protective.