Showers and Fresh Clothes

My husband has dementia after brain damage in 2011. He is generally easy to deal with, but I really struggle with getting him to take a shower. He has a seat and hand/held shower. I’ve asked if he wants help. No.
How can I motivate him to shower? I don’t believe he would ever do it, otherwise. If his hair needs to be cut, I insist he shower, first. If he has a doctor’s appointment, he usually can be convinced to shower. At Christmas, when we were going to my daughter’s house, he showered. On a regular basis, I am lucky to get him to shower, once a week.
I mentioned clothing, too. He does choose fresh underwear, but otherwise wears the same thing every day, even if he has gotten food on himself. Any help would be appreciated. He is mobile enough to do these things. I don’t know what to do!