Here are some items that Wilbur likes/we've talked about that I've recommended for you. Hopefully having them all in one spot will make it easier for you!
*I am affiliated with Amazon, so if you do purchase anything through these links I will get a percentage. Thank you!
Remember, this is not something a dog will learn quickly. Unfortunately, it is a bad habit. Bad habits are hard to break, and the longer they've been getting away with it, the harder it is to break. Be consistent, every person your dog comes in contact with while learning needs to follow the same rules.