Plant different species and you will be OK saving seed. This is what I will probably do on the pole beans. Mix yard longs (asian green beans same family as cow peas), runner beans (scarlet), and one of my favorite P. vulgaris poles, either wax, purple peacock or kentucky wonders (only one of the 3). Good luck with your garden!

Also, if you aren't concerned with saving pure seed, you can mix them to your heart's content. Over the years I've seed a couple of people, mainly from indigenous or Appalachian roots, who kept a "bean jar" with several kinds of bean seed, all mixed. They simply planted them, every year, as they came out of the jar. These folk didn't consider any resulting crosses as bad.

George
Tahlequah, OK