I have this problem more with acrylic stemmed pipes than anything because they are so hard and slick. I am a button biter, and I probably have a nice spot worn in both molars right behind my eye teeth. It's one of the reasons I can't do P-Lip pipes because they are rounded and slide all over the place. Also the shape of them just kinda unsettles me.
I also recommend softie bits. I put them on most of my pipes, and they do make clenching easier. Some people find them aesthetically displeasing, but they don't bother me in the slightest in that regard. You may also want to invest in pipes that are light and distribute the weight in a way that is comfortable for long periods of clenching. A Stanwell featherweight, for example.
That is true, at least the good ones only come in black. I have seen clear ones before. Luckily, they only cover the bit which is hidden in your mouth while smoking.
I clench that way. Rest the bottom of stem on bottom lip, and the button is parked on top teeth. When I'm sitting down, it works very well, but walking around can get dicey. So when I'm lunting, sometimes I use both upper and bottom teeth. Just sorta balanced between teeth that I'm not biting on the stem.
You could go with some silicone tape. It comes in black. Holds bite marks. It’s great stuff. I use 3 to 5 wraps around the pipe. Great for clinchers and even better for stem protection.
I wish I could offer some good advice on this, but all I can think of are some goofy, smart-ass suggestions. Therefore I'm not going to post in this thread.