How to prevent pregnancy without leaving my dog at home?

I spend the night at my fathers on Saturdays and usually go over for a few hours one or two other days as well. My 11 month old dog goes with me, and after an initially rocky start, has made best friends with my dad's 6 month old yorkie. They go crazy for each other and she looks downright depressed for a while when we go back to my moms. i hear he does too after she leaves. On Saturdays she sees me packing up her food and toys and goes nuts. The only problem is she's a 7.4 lb Pom/chi and Teddy is a 3 lb yorkie and neither are fixed and they never will be due to health reasons. I really don't want to leave her home since she's due to go into heat soon, and would hate to keep them separated if I did take her. She has no other close doggy friends and just lives with two crotchety old cats. Teddy has no friends either and lives with a two large 13 year old neutered dogs and a cat, so he has no playmates at all either besides her. Would it work to put a sanitary diaper on her or a belly band on him? I am also not willing to use medical means of birth control as they raise the risk of canine mammary cancer, but I have absolutely NO intention of ever letting them breed