Wood floors expand and contract, so even if you were to coat them with a new poly coating, it would crack between the boards in short order. Sorry, but you should lay down loose lay vinyl sheet flooring and confine the dogs to that room if you anticipate accidents. Wood floors are damaged by pet urine, and your friend has the right to expect that to NOT happen to her home.

Water bourne urethanes have a lower VOC than your oil based polyurethanes. It does dry quicker but no real way to speed it up. Be prepared to wait at least 5 hours (depending on brand) before you can walk.

If youre dog is going to have accidents inside refinishing the floors wont make a difference. The only thing sanding them now will do is determine which spots are because of your pets when you move out.

If you dont own the house its not youre call when they or if they get refinished.

Urethane by its self wont fill gaps in the floor. A wood filler will fill gaps but as it was mentioned previously. Wood expands and contracts so good chance not all the filler will stick(dependon the size if gaps)

Water borne finish doesn't have an objectionable smell to most people. It dries fairly quickly and there's nothing that will make it dry faster. If you want the cracks filled, they could be filled during the sanding process. Refinishing the floor and filling the cracks would not render the floor impervious to dog urine.

See I thought that refinishing them sealed them. Learn something new. Not just my dogs (although I'm paranoid) but any water I'm worried about with kids and stuff..crap happens. Good then, I'll save my money for something else then.

If you catch the spills or dog urine fas enough then no worrys. Refinish will seal the floors. But the problem is when your out and the dog has an accident and you dont catch it for hours or even days.

Doesnt matter if you have 1 coat or 100 coats of finish. Any liquid if allowed to sut long enough will penetrate.