I would purchase an area rug pad...its more to protect the wood and keep the carpet from walking more than anything. Have an area rug custom made out of a good value carpet. Wont cost that much. Have it bound and created fairly close to wall to wall so that the wood will not age at a different rate than the covered wood. this is the only way to protect your wood...and do not let them pee on the carpet as bigger dogs pack a volume of urine and can ruin the hardwoods. Not any great answers for you....good luck!

Thanks for the suggestion. Is there a particular type of material we should look for in the rug pad? Again, my fear is that the pad itself will scratch the wood floor under it.

You HAVE to use the correct type of pad, and then not let grit get down between the pad and the floor. Call the hardwood floor experts in your area. If you are careful in what you put down, keep it clean and dry, I think it will work.

Here's an article I found when wondering the same thing.

Here is a link that might be useful: Pad for on top of Hardwood

Soft Paws!
One of my dogs was scratching at doors and would open the doors with the lever handles. At least Soft Paws kept him from scratching the wood, even if they did not stop him from opening the doors.

You glue them on. It is not the best solution in the world, but it does protect the floors. You might be able to put up with them for the five or six months you need to. I found that some stuck very well, and really had to work hard to get them off when it was time to replace them. Others fell off early. I did end up trimming his nails with the stuck-on ones still on. The vinyl did continue to help somewhat, even with the tip cut off.

Here is a link that might be useful: Soft Paws FAQs

Keep their nails well trimmed and then file the cut edges round.

I would also suggest that in this situation, your best bet is going to be diligent and I mean weekly nail care for the three dogs. Keep them extremely short and you shouldn't have a problem but you will have to trim and file every week, no exceptions. That's a lot of work. I would be afraid of putting a rug down and then a dog pees and you don't know it so it sits both in the rug and on the floor. Or you spill something and that too sits on the carpet. Dirt and grime will work through the carpet to the pad so you will need to roll that rug up at least once a week, with three dogs dragging debris in on their feet I would suggest at least twice a week rolling up the rug and cleaning the pad and then rolling up the pad and cleaning the floor.

You couldn't find another house to rent that didn't have hardwood floors? ;-)

Our home had hardwood floors with 2 big dogs (75lbs each) and the only thing that hurt it was their nails. We had remnants on the floor for a while and area rugs without a pad underneath for 7 years. When we pulled them up, there was zero damage to the floor. The dogs did have accidents on the floors from time to time, but we never saw any warping or other damage.

If the floors are in good shape and are sealed effectively, you should be fine. That said, I would suggest a large remnant with a pad underneath since these aren't YOUR floors. I don't think having the pad 'an inch short' is going to do THAT much damage. If you have a LARGE remnant and furniture is on it, it won't be sliding around to cause friction (it's the friction that does the damage). And how frequently do you walk the perimeter of the room? Maybe make sure that the pad continues to the edge or the rug in the door ways, but the whole room is silly.

Thanks all for these helpful commments. I followed the link about padding for hardwood floors and was pleased to see that rebond polyurethane is recommended since it is cheap. Someone gave us some nice free carpet remnants and some nice-looking polyurethane padding with one coated side, but for some reason that padding has a strong chemical smell, so I guess we will have to bite the bullet and actually put out some cash for new padding. I'm intrigued by the idea of using another area rug as padding for this carpet, but it sounds expensive and too thick!

In answer to the question of whether we couldn't have rented a place without hardwood, what a sensible question :-) But actually, we were really lucky to rent a place at all with three large dogs! And our rental happens to be right across the street from the house we're remodeling! So no, we didn't have another option anywhere near this attractive.

I wouldn't risk just clipping the dogs' nails in this situation to protect the wood, so a pad under our temporary carpet it shall be. The advice to roll up the carpet periodically to remove carried-in dirt is obviously from a fellow experienced dog owner :-) and is very well-taken.

Fortunately, our dogs are all very reliable in terms of housebreaking so we don't expect any problems in that area.

Thank you all so much for your kind input!

Make sure you file the cut edges after cutting the nails.

The cutters leave very sharp edges on the nail.