I have several Oak trees with a hollow spot that might cause it to break and fall. These trees are in an area around my house that are key locations one being the main shade over my deck. Removal is going to be my last resort. Has anyone had success repiring a problem like this? Thanks.

You would be well off to call an arborist and get his on-site opinion. I have a friend with a huge oak in his backyard. There is a hole large enough for kids to climb inside and up to an opening higher in the tree. A previous owner stopped by one day and said he used to climb in that hole when he was a kid, he's 52. Hollow limbs I would cut of right now, ro repair for them .

If spots are small. Not sure what small is. I've successfully patched about 6" x 6" or so and juste recently a small hole compared to the tree trunk with Rockite and then covered with two layers of tree wound dressing.

Rockite is an expansion cement available at a hardware store.

Durable repair, but you have to make sure all of the rotten wood is removed and bugs are killed.