Ahh good times with this game.
This was my first flash game I played when I first visited this great site. I don't see how these 2 before me didn't enjoy it. I got up to 100 Tower guards and Repair men with maximum upgrades for the turrets and the barricades.
The only problem I saw with this game was that I couldn't repair the box or fort. I spent the money...but after I clicked the new level to start my health just went back to what it was. Got to level 35. Great game.