There are several tools out there, the most well known one being Originality (full list here). OpenAI is also working on tools to fingerprint content generated through their tools. Ultimately, I don't think this is a winnable battle (students can do multiple rounds of rewriting with different tools until the fingerprint is gone). But hopefully I'm wrong. If not, the best way to handle it is to update our education system to incorporate the new tools, just like we did when calculators came along. I remember my math teacher saying "You won't always have a calculator in your pocket!". That didn't age well.