Doodad Walls?

[Pahl]

So im on the process of creating a basic "zergling rush at your terran base" map just to get a hang of this editor. And i want to use the doodad-walls to fortify a position. However it seems units can just walk through the walls.
How do i make the walls solid?
The specific doodad is "Structures>Metal Wall"

 

[themean]

add footprint

 

[Pahl]

Care to expand on that? It might be something easy im overlooking/not finding, but in that case it should be easy to explain too.

 

[themean]

in data editor actors tab search for metal wall
click on metal wall
http://www.thehelper.net/forums/attachment.php?attachmentid=37423&stc=1&d=1280769942
after that search for actor-Footprint
add your own footprint