I once had this problem and spent a lot of time cleaning the cedars out.
First thing I did was walk down the property with a large set of pruning shears and cut all the small stuff down.
Then I sold the large trees for fence posts:
Advertise something like: "Cedar Fence Posts. $1.00 per foot. You cut, You haul, You Stack the limbs."
If they are too small for posts, and too large to cut by shears, wait for the first snow and burn them, again and again and again....
It takes a lot of weekends but its worth it otherwise they will take completely over.
