Neutered males will still show interest thrughout the heat cycle, and are ready, willing, and able to "do the deed" when your bitch is ready. While this won't result in puppies, it should be prevented, as she could get an infection. You must keep them separated. Crate your bitch, and crate your male, too, when not under your immediate supervision, and whenever you have to leave the house. Crate both because it's possible for them to mate through the crate - especially if you have wire crates - and could result in injury.
Get a couple pair of bitches britches (or sani panties, whatever! lol). You don't have to buy the pads for dogs, you can use use those made for women. Panty liners should probably work for a first heat, but if she's bleeding heavily, you may need a regular pad.
Whoops, forgot about your male's marking behavior! Just treat it like a housetraining issue (when you can't supervise him directly, contain him). A couple of days of watching him closely and getting him outside when he lifts his leg should do it. Just keep a close watch on him so you can prevent him from marking, and hustle him outside.
Expect to see some clingy behavior from your little girl, and she might get snappy with your male if he starts sniffing around.
