Excellent suggestion Hortensia!
Also you can use their own letters to Bodies of Elders by mentioning your sign and amending it to read NO TRESSPASSING, ESPECIALLY NO UNINVITED RELIGIOUS VISITORS.
Once you have the NO TRESSPASSING sign up the decision of the elder to visit will involve a lot more than a personal choice, momma Watchtower, has written Bodies of Elders saying that any JW who willingly TRESPASSES onto property that is so posted will be on their own, they may incur fines and jail time, and there'll be no Brooklyn legal Dept support for such cases.
If he insists on staying, record the conversation with a videocam or a digital voice recorder (a lot of MP3 players can record too).
Write a letter to the KH as suggested and send a copy to the PO and to Brooklyn, requesting to be put on a permanent DO NOT CALL LIST.
Keep threatening legal action and put a restraining order against any JW that dares give you a strange/evil look.
--ILOOWY