Sorry, there's no impenetrable defense.
However you can be very strategic, the goal in making good defenses is to make the attacker run out of time typically.
Any truly skilled raider will pick apart any defense eventually, but here is a couple tips,
1. Keep all survivors near eachother, so if one is attacked, all will fire back so they aren't picked off easily.
2. Better weapons and gear always improves your chances obviously.
3. Be mindful of people throwing nades at your buildings especially from the inside of your compound
4. Place your traps smartly don't make it so obvious, think like the raider not the defender when building a defense.
5. Raid practice is perfect to test your defense, i recommend getting more raid experience, if you come across a particularly difficult defense take notes.
Edit: change things around a little every few days or wars, change positioning or traps to keep your defense fresh there's nothing worse than a defense that has already been figured out and you know where every defender and trap is.
Edited by Cybertraxx, 04 May 2016 - 01:43 AM.