There should be some kind of a message before you confirm turning to non peaceful. It should provide players information and warning that they should only turn non peaceful if they know what they are doing, have a decent fortress (some link to images and examples), to check one more time how wars work and maybe even some examples of wars in the past, and finally warning them about other nearby towns needing to be 8 chunks away or more and anything else that might be useful for players. There has been quite a number of people that make normal towns and turn them non peaceful recently
Either when they type the command to turn non peaceful or a rotating message every now and then like how it did for ships and tanks.
Another way to prevent new people from turning non peaceful might be to make a check if they have at least like 100k blocks with HP but that might not be doable or might be intensive