I've seen one homestead, in South Africa, built with think stone walls, with slits for the rifles, a well inside and food for about 30 or so, for nearly a year. I was invited to join if anything happened (at time white gov stepped down.
The problem you mention is immense, but it might work out in the sense that bands will extract a 'tax' in foods etc for protecting a number of such homesteads...
I am not familiar with Africa, but hopeful that would help them defend. Here in the U.S. they have to many weapons that would lay waste to stone walls.
It is an immense problem, one I hope never comes and is just the worries of an aging man who sees to much corruption and allows his mind to worry to much.