I have a 6 month old rottweiler and he started shewing on furniture, wall trims etc. when he's new teeth were coming out, so I understood (not that I was happy about it:)

I ended up getting one of those sprays and I think it helped a bit, but now he has all new teeth, plenty of chew toys yet he still chews on all wooden furniture, wall/door/window trim etc.

I have to replace all the trimming on the first floor but before I do I'd like to make sure he doesn't do destroys it again.

Anything you can recommend? Maybe some better spray, something that lasts longer..

I know how bad that spray tastes, as I was spraying it got into my mouth and for the whole day I could taste how bitter it is.. but it doesn't last long on furniture/trim so after a few days he starts shewing again.

Also, I'll have him fixed soon, should that help?

Neutering won't stop chewing.

When is he doing this damage? If it's when you aren't home he may very well need to be crated.

If it's when you are home, he needs to be watched more closely.

Sounds like a bored puppy has developed a bad habit. Maybe some positive reinforcement, like a kong toy with treats inside, might work better than the bitter spray.

I'd also recommend a LOT more exercise. A six month old Rottie can do 15 miles in an afternoon at a trot and not even notice. I'm not recommending that much, but he needs to get tired.