A number of years ago, I had a student who had the nerve to turn in a photo copy
of the solutions manual for his homework. I asked where he got it from and he
told me that it came from our on campus tutoring center. He was shocked when I
told him that I would not accept it. Then, I went to the tutoring center and
confiscated their solutions manuals, which they said were only there to consult
if the tutors got stuck (they had asked the department to provide them for that
purpose).
In the next term, I quit assigning homework. I went to recommended problem
lists. I relied heavily on this list for my tests/final material. Of course,
I had to laugh when a few students complained that they had no idea where I
could have gotten these test questions and that they certainly weren't related
to the course.