Can I politely stop an AI's Great Prophet from getting to my cities?

The strongest player in the game is a close ally of mine and we each founded and follow of one of the strongest two religions in the game, with little cross-over between religions within our territories.

I've just spotted that he has a Great Prophet approaching my territory. According to the Civopedia they are powerful at spreading religion, and I'd rather not have a huge hit to the followers of my religion in my cities.

How can I prevent another players Great Prophet from damaging the religion in my cities, preferably without causing a major diplomatic incident.

Solution 1:

Station an inquisitor/inquisitors in your city/cities and he will be unable to act. Alternatively you should be able to surround the city with 6 workers/other non-combats (triangle units) and he won't be able to get close enough to use his ability.

If he does successfully convert some citizens, you can use an inquisitor to remove his influence, but its preferable to block him by just stationing the inquisitor there.

I don't believe any of those will cause a diplomatic hit. If one of them does, it would be using the inquisitor to remove influence after the GP is used on a city.

Solution 2:

Agreed. You have to block him out with units. if at all possible I would try to surround him within your territory or pin him against a coast until your open borders agreement runs out. That way the AI can't target a new city. Using the inquisitor never affects influence because you can only use it within your territory. In the future offer money for open borders instead of open borders for open borders.