Here's an idea. If you want to slow down a base capture. Why not add rings of barbed wire/tank traps. These are all destroyable and the attackers need to blow them up in order to allow troops to run through the gaps. If you blow the wires sporadicly instead of blowing it in one straight path, the troops will run around in circles until they find an opening, then again and again until they reach the map room. If you blow the wires all parallel to one another, the troops will just run a straight path to the map room.
Adds a little bit more decision making and slow it down just a wee bit more.