A wall is only going to work if there are machine guns on top of it and the will to use them. IMHO.Nascar only runs so many days a week for entertainment.
I think refreshments, paint balls, rock salt , etc. given to bored kids or other interested volunteers would work.
If the volunteers were shot at with live ammo, let them defend themselves.
An effective and entertaining method both to those working the fence and those who would like to watch.
This is of course with appropriate protection to protect them while passing time among friends.
The cost of maintaining the fence/border would be minimal.
I didn’t say I wanted to shoot our friends south of the border, even with paint balls. LOL! I’d rather make employers be more careful about who they hired, for a start. I employ 2 Mexicans and they are both legal. I have a landscape crew that takes care of the yard and I am sure some of not most of them are illegal but the boss is an American born Mexican and he hires the others, not me. I have my doubts about a fence.