It isn’t the first time someone built a heavily trapped, walled and patrolled border of that size.

Take a look at the Inner German Border. It was over 1300 km (approx. 810 mi) long, and was (average) about 5.5 km wide (a bit more than 3 miles).

From 1974 to 1979, 4956 people attempted to cross it, and only 229 (4.6%) actually made it.

Edited my comment to fix, thanks!

This is less of a source and more like a compilation of resources, but for anything spacecraft related I can always recommend Atomic Rockets. For this specifically, the page on Heat Radiators.