Gosh, those dogs are the worst! Every once in a while I get a dog who just pees EVERYWHERE because he feels like it, and it is so hard to prevent it (because they're not your dog, so by the time you get any "training" done, it's time for them to go home). It doesn't matter how many times they are out to use the restroom: they pee in the house because they want everything to smell like them, and to claim it as their space ("this couch is mine, this is a nice table--better pee on that; that's mine too"). I even had a dog pee on a chair leg WHILE my husband was sitting in it lol
There are a few different things you can do to save your house. The first option is to do crate training. Crate them when you are too busy to chase them around the house, and let them out for feeding, and potty breaks. Option two is to tie a long training leash around your waist, so you can catch them in the act and correct them every single time. It's hard to stop a determined marker without a lot of training, and by the time you get them to stop, they won't even be in your house anymore, so it's up to you to decide how much work you want to put in to them.
I'm impressed that Karen R. got a client to supply belly bands! I have dogs pee right in front of their owners, and they are embarrassed but don't really try to correct it. Some don't even apologize. "Oh, I think he peed. Okay, gotta go!" That being said, its up to you whether you want to mention it to them. It's hard to do it without openly complaining, and after several days of cleaning pee, it has a good chance of coming out that way.
In the mean time, I recommend a good enzymatic cleaner to get that smell out for good. My favorite brands so far are the "OUT!" brand spray in the Walmart pet section, and Nature's Remedy. Both are good. Do not buy Clorox Urine, as it makes the whole house smell like ammonia, which is totally awful and makes the pee smell even stronger. (yikes!)
Let us know what you end up doing!