Hot take: if your students are "cheating", it means they do not see the value of the process of doing the exercise and see value only in the grade they obtain thereby. And if that is the case, at least part of the problem is that you as the teacher (and probably to a larger extent the education system as a whole) have failed to adequately communicate why the exercise is valuable over and above the grade (and more than likely failed to adequately establish that value in the first place)