If the wood expandable gate is a good fit, you could pad the areas that touch the woodwork. Moleskin from the drug store would work.

If the dog is not determined, a large piece of stiff cardboard will work.

We have a baby gate that we picked up when the pups were in house training. We stored it away and brought it out last week to block the stairs so Cooper can't go up while he is recuperating from surgery.

We used to wrap a towel around the wood banister then tie the gate to the towel. The other side was attached to the wall. We didn't damage the wood that way.

We also use an expandable baby gate. (It is as old as my "baby," that is, about 25 years old.

For a few dollars you can find plumbing foam pipe insulation that just slips on and protects the woodwork. See link below.

It has also been very useful on vacation at the beach to keep the dogs on the deck or confined to part of the house.

Here is a link that might be useful: Plumbing pipe insulation