Let's implement a hard badge where you have to quit when you lose one life but as a developer I won't add a quit to menu or restart button in the pause menu... brilliant.
To get the badge: spend every dollar on weapon SPEED upgrade until it is maxed, then buy 4 mines place one on each side of your base. Keep your health up and try to start each round above 75/100. Weapon Damage is a useless upgrade, and increasing max health won't be needed if you max weapon speed and have good aim. Easy game, pretty boring really.