Wander Restriction?

[Sashimi]

Hello,
I was wondering if there was a way to give units with "wander" ability a restricted area in which they can go?
For example, on my map, I have a swamp.
In the swamp, there are a couple of frogs.
They have wander, but I only want them to wander around within the swamp.

How can I do this?
Thanks in advance!

 

[WraithSeeker]

Make the swamp a region, and detect when the frog leaves the region, order the unit to move to a random point within a region.

 

[Sashimi]

Hmm..
I'll try that