Making a door object invisible

[Auxie]

Hi folks,

I am using doors objects (barrels) in a zone to keep people from physically being able to run out of a holding pen sort of area and requires them to talk to an NPC to teleport them into the area outside of the barrels.

I was wondering though, to keep folks from levitating etc to get around the barrels I had to make their size 4000 in the DB. This unfortunately has made this holding pen area feel like you are at the bottom of a huge well and kind of daunting. Is there a way to make objects invisible so you can't run through them but you can see through them?

Thanks.