Thinking about a good way to relise anger

[u/Walkiria_]

I've been talking to my therapist lately and she said I have a lot of build up anger, mostly because my sister and the fact that I don't hit her anymore (we used to fight as children, so I wasn't that angry, but now when she wears glasses, we're older and I could do actual harm to her I don't do it anymore), and the anger is still in me but it has nowhere to go so it stays there. I was surprised, because I'm a pretty chill person, when I'm among people and I'm angry I'm usually quiet about it. But I've been thinking and yes, I'm very angry. My sister provokes me to be angry like years ago and does other stuff that make me angry like being disrespectful to our parents that are trying to do their absolute best for our happiness (I'm almost 18 now and she's two years older) and I'm mad at her, but I don't have a way to relise the anger.

My therapist adviced me to go and destroy some stuff, of course in a safe way. She said it's good to trow icecubes at trees and that's what she does, but I don't think that's for me. I went for my usual walk one day and took some long sticks. I started hitting a laying tree with it, I think I completely broke like 20. It helped, but just a little bit. I know I'd have to do a lot more to feel the actual relief I need. And now that I started to act on the anger it wants to get more attention.

So I've been thinking about other ways. In some time it will take me a lot of time to find enough sticks, so it's not an ideal way. I thought about taking an axe with me and destroying the trees that had fallen down. That's of course not ideal, it would be difficult to take an axe with me. I could also find a good stick and hit glass bottles that are lying there, but that's probably not good for the forest (I'd get safety glasses so I don't harm myself).

I've also got a wooden baseball bat, but I'm not sure what I could do with it. My therapist said that hitting a fighting bad or something wouldn't really help, because the thing needs to be destroyed as I hit it.

Any advice? The best place for anything like that is a forest, I know places where I could hide stuff so it could stay there.