nostr:nprofile1qy2hwumn8ghj7un9d3shjtnyd968gmewwp6kyqpqn7dnfh74anaddchjhrklj7yumhz3k3yqe93m6a2ug9gpdulc8l6s09j7u7 Why not disable the search function for guests? You can find the relevant setting in the admin panel.

nostr:nprofile1qy2hwumn8ghj7un9d3shjtnyd968gmewwp6kyqpqn7dnfh74anaddchjhrklj7yumhz3k3yqe93m6a2ug9gpdulc8l6s09j7u7 You could use fail2ban. Idea: block any IP that calls /search?tag= more than 30 times a minute (that would be a query every 2 seconds) for 10 Minutes or so.