Knowing that cloisters can have this effect is half the battle.

Rather than adding a house rule to a very popular game I would advise you to alter your strategy a bit to account for future cloisters that you may not control.

Examples:


Leave a good cloister spot next to an open road that you own.  
When considering placing a tile between two relatively equal spots determine if one or the other creates a better cloister opportunity.
Keep track of how many have been played!  If you get down to 10 tiles left and 4 of them are cloisters, make sure you have the meeples available to use them.  Alternatively, keep your opponent from freeing his meeples from the board.


House rules to make the cloister less of a game winning tile in Carcassonne?
Why do some people have the custom to wind the Tefillin-Shel-Yad towards themselves, while others wind it away from themselves? What is the reason behind these two customs, and which sects of Judaism generally follow which method?
