The garage has a tower over it, as does each corner- These have independent turrets running on solar and batteries in case the main defensive turrets go down due to running low on fuel and battery charge. Each wall has a shotgun turret every five meters and it has two different heights so defenders can be on either height should the situation call for it. The third layer of defence is a field of spikes, which do damage and are easily replaced for little cost. The second layer consists of barbed wire fences just behind the electric fence, partly to slow the entities being shocked down and to add additional trap damage, while also giving the next layers of defence more time to dispatch hostiles. When the motion trackers see movement from either of those things, it will electrify the fence and sound an audible alarm. The outermost defense mechanism is an electrified fence, which activates on zombies or non-allied players getting close. The fortress is mainly made up of scrap iron reinforced frame blocks, which could be upgraded with concrete.
This is a simple savegame, I manually built the fortress myself after spawning in a burnt house near Perishton.