The explosive mines and barrels and such should have the ability to set a timer before they detonate. It would give bases the ability to defend against the more experienced attackers that use one or two troops to clear the entire path to the rest of the defenses and then send in ungodly amounts of high level troops. If it would upset the game play too much maybe make it an unlockable feature for upgrading these units. Maybe even make each upgrade unlock a longer timer length.
