This is what we did for our trees/cats:
We get live trees.
1. Bring in tree and set up undecorated.
2. Let the cats/dog check it out under supervision. BTW we get the trees with "points" and not the soft needle kind - works well to keep them away after they get poked a few times.
3. If they attempt to touch or climb they are told NO in a loud voice. Most times this works.
4. Spooky was bored with the tree - seen them too many times. Ling never saw a tree so this is how we got her to stay away.
5. Sit quietly with the water spray bottle. Wait for cat to come near the tree and then without a word have the tree "spray" water at the cat. They don't know what hit them other then to know the tree is not a good thing to be around.
6. Took us about 4 times of the tree attacking the cat (Ling) for her to avoid that tree.
7. When decorated you might have to reinforce the water thing once or twice.
8. Be sure to hang unbreakable stuff near the bottom and do NOT use any of the string tinsel on the tree unless the tree is totally off bounds to the pets (like behind closed doors).