An obvious solution is to require the use of Google docs and include the history as part of the assignment. If there is no sign of sentence restructuring then fail the assignment.
This is the equivalent of asking students to show their work when they do math problems and that is how we thwarted those evil calculators.
This is likely easily gamed by asking the LLM to provide a number of intermediate versions of the output. You still have to do some yak shaving in google docs, but nothing too hard.
I wrote a blog [1] a couple years ago about this solution - it turns out it is possible to use timestamp authority servers in combination with hashing functions to create a verified edit history. Like the other comment said, it merely starts an arms race where the AI side is likely to win, which is why I haven't pursued this further.
For something like digital art creation verifying the edit history is much more fruitful since the diffusion process is nothing like how humans create art.
Google docs probably isn’t even the best tool for the job, blackboard or one of the other edu mafia platforms will build some sort of halfway decent app that will check for typing vs just copy pasting as well as other indicators.
This is the equivalent of asking students to show their work when they do math problems and that is how we thwarted those evil calculators.