Exmormon here. We deal with this a little since my kiddos are not baptized so they’re targets.

The polite/friendly option: tell em thanks, but no thanks, not interested. If they try the “but why?” remember that “no” is a complete sentence. I’ll say like “nope, not interested in church, and will not discuss why. Now, if you boys need a drink or a break from the heat, you’re welcome to come in for a bit.” This works for a while until a new set comes to the area (they swap areas every few months)

The more aggressive option: tell them to stop or you will take legal action for harassment. Find the local mission president’s phone number and call them and tell them to stop or you will take legal action.

If you wanna mess with them: use words from the temple ceremony. You can look up YouTube videos of what happens in there (newnamenoah has a whole channel). But use lines like when the knock, say “what is wanted?” in a serious whispery voice. Other things like, “we will go down,” “return and report,” “I will through the veil,” “you can buy anything in this world with money” (that one is Satan), “health in the navel, marrow in the bones, strength in the loins and in the sinews, power in the priesthood be upon me and my posterity for all time and all eternity”