i have a mimosa tree that i planted from seed 3 years ago its over 4 feet tall now. They are very fast growing from what i hear (im in canada) Not sure how invasive they are though. Their flowers are like pink puff balls very nice. first think i will plant when i move down there, i live this tree.

Apple,

Where are you located? How large of a tree do you want? What is your soil like?

You don't want a mimosa in Alabama! They're very invasive here. Also, you might want to put the tree outside the fence if you can, depending on the temperament and activity level of the dogs. We have a pretty big back yard, but over the years we've had small trees dug up by one dog and others "debarked" by another dog.

Do tell us more about where you live and whether you want a big tree like an oak or something smaller like a cherry tree.

More importantly,

Do your pets have access to shade now? If not, please don't wait for a tree to provide it - they may die of skin cancer by then.

I have a solid-white, blue-eyed feline companion. His ears must be rubbed down with sun-screen each day before letting him outside.

Nelson

Yes, they have shade right now, but I am wanting to put a tree in their area that would eventually shade in almost the whole area. I do not want a mimosa, they are invasive. They are almost as bad as privet hedge. I am looking for a fast grower.

I would suggest researching trees that are not poisonous to dogs. The leaves and fruits of some trees, cherry laurel for example, can be toxic to some animals.

I found a website that is very helpful. It was put together by the Animal Poison Control Center. Thanks for the suggestion!

You don't say how large the dogs' pen is, but you might want to leave them some sun for cool days if there's room. Our dogs love to sun themselves in the Spring and Fall. Have you considered things like a cherry tree, which would be ornament as well as useful?