[capt_noonie]

I've never heard of such a thing. If the female is old enough for spaying (around 8 months) I would do it asap. Yes females mark, but if you empty their tank before they can mark, there will be no scent. Take them out frequently for walks or at least breaks on schedule. Get them used to the routine as early as you can. Uni is spayed and has marked indoors two times that I can think of, both times was before she had "siblings". Once when I first gave her a Wishbone chew (guess she loved it so much she didn't want anyone else to have it), and another time when we went over to a friend's house and she marked on the other yorkie girl's bed! No clue why, but she did.