The only real way to block specifically openAI generated content (or some other online generated LLM content) is for the company itself to store all of its outputs and compare to that database, like shingling / LSH for plagiarism detection. Other LLMs (local) are completely impossible to block, as it's a constant chase. Any system that tries to estimate the distribution of e.g. a specific LLM that performs beam search with certain parameters, can be easily adjusted to use typical decoding or something else, so it simply will never be possible, hence useless to try to stop.