My choice is forested areas or deep mountains areas with a lot of bottle necking gaps. Preferably both. The thick trees and vegetation would provide a good curtain to hide a large group hidden deep inside. A mountains area would give strong natural barriers. The incline would slow them down. They may not even travel uphill. They may simply follow the path of lease resistance. You could probably set the terrain up to you advantage. And the bottlenecks being rigged with explosives could slow them down and thin their numbers in case an escape is needed.