My 8 month old rottweiler puppy chews everything, how can I stop him?

You cannot stop his chewing, but what you can do is give him something he is allowed to chew – something more tasty and/or interesting than the valuable items you don’t want him to destroy. You can ask the butcher at your market for some bones. Or get a Kong; they’re great. Make sure he always has something like this available – preferably 2 or 3. And if you catch him chewing something you don’t want destroyed, just redirect his attention to the bone/Kong.

^ Yep, great advice. Kongs are saving my furniture and my puppy’s life on a daily basis. What I would add is that there is no need to feed a dog from a bowl. Gulping down a bowl of kibble takes most dogs about ten seconds. Once they are done with that, many of them spend hours getting more and more bored. I feed my dogs by stuffing Kongs for them, and they love it. By drawing out the process of eating, you’d be giving your dog something to do. Something fun, which he can do all by himself.

As a handy by-product, chewing reduces anxiety. Thus, Kongs are self-rewarding, and dogs very quickly learn to love them.

You can also put hot pepper concentrate on things you can’t put up

I stuffed Kongs with a mixture of wet and dry gourmet food and froze them once he learned to use them. That draws out the time it takes. There are also many organic chews like pig’s ears that dogs like. However, Frodo did continue to chew other things too. Bitter Apple spray can be used on furniture legs and baseboards and can sometimes deter a chewer.

You can also start training him with the words leave it. Every time he leaves the item you told him to leave, give him a treat. Eventually he will relate to leaving the item you don’t want him to chew with something that is desirable by you. Dogs aim to please and eventually he will lose interest in chewing them.
As @wildpotato mention, it is also good to direct him to something that is desirable to chew. My dog was a chewer and she has done pretty well with dura bones. They have different flavors one. It can take a few months. It did with my dog but I think it was because we got her at 18 months of age and no one ever bothered to correct her before. She now looks for her bones whenever she has an urge to chew.

If nothing above works, or in the process, you can by this spray that makes things taste bitter. Avoid the pepper idea because it can injure the dog if it gets in its eyes and if you have kids it can hurt them, but the bitter spray is non toxic