[meyer]

I like that idea for a wall, but with 50 cal machine gun nests every 200 yards and the occasional, random flyover by an A10 Warthog loaded for bear. Maybe precision artillery too - to make it fun.

[numberonepal]

I could build it coast to coast for $3 billion.

[numberonepal]

I could build it coast to coast for $3 billion.

[Axenolith]

Cost!

Moat/canal on all the relatively flat stretches, barb wire/chain link each side, Nile Crocodiles...