I am unsure if carving into a tree will assist in protecting? What type of protection are you seeking-from fire, damage,illness, or something else? Perhaps the best method is using paper or crystals for protection as well as fallen branches to carve on.
Then comes to the question what beliefs you have? If I tell you to use symbol "Algiz" it might mean nothing to you and if you do not have the intent or energy or willpower and knowledge. Whatever I say in symbols is useless.
If you provide mor information I may be of more assistance.
I'd appricate if you would give proper information I can use- Stating Polytheist is very vague. I have no idea of your standing in anything. If you are seeking protection look up Algiz if you like and see if it works. As I do not know your practice or what you have done in your history. Burying certain stones can assist with protection. I will lastly, suggest to study and find what you feel is right.
There are a number of runic symbols that could be used as methods of protection. However, remember that runes are associated with the Nordic religions and those religions do not contain such concepts as "demons" or "hellhounds" so whether they will be the best choice is doubtful. I'll note that demons and hellhounds are not part of Wiccan beliefs either.
Rather than use runes to protect against beings drawn from the Abrahamic religions, I would suggest you looking into the Seals of Solomon. You can find images for them at http://www.empireamulets.com/the-44-king-solomon-seals.html
And if you're looking into protecting an area of forest I would not carve the symbols into a tree. Doing that damages the bark and may cause the tree to become diseased or invaded by harmful insects. Try painting them on a stone and then burying the stone beneate a tree or along the edges of the area you wish to protect.
Thanks i will search it right now. Also i asked about the demons because i want to be prepared for the Apocalypse, me and my friends have made a coven and we are learning kinetic abilitis, i learn geokinesis.
The Apocalypse is a belief in the Abrahamic Traditions. Wiccans do not believe that such a thing will happen. So if you're Wiccan you have nothing to worry about.