What do you do when your students keep using AI to do homework and assignments?

Over the last two years, assigning homework to students has become futile. They go to any AI tool to find answers; they only do copy-paste without even reading. To teachers, AI's responses are very recognizable. But the main dilemma is what about students' skills? How can we evaluate their skills in the existence of AI, especially when we have online students?
I'd love to hear from you :)