This - I think part of the issue is to stop homework from becoming busywork for grades. If everyone has the understanding that this is supposed to nail down and

This - I think part of the issue is to stop homework from becoming busywork for grades. If everyone has the understanding that this is supposed to nail down and self-test understanding of material taught in class, then there's no reason students should "cheat". To this end, I like the approach of mentioning repeatedly that homeworks are for the students' own good, then give a test early on to make students quickly understand they'll do badly without practice, and then announce after the test that you'll drop the scores, but just DO YOUR DAMN HOMEWORK! :-)