If you want to be extra cautious, you can leave a slow zombie alive at the end of a wave, and run around repairing all of the barricades before killing it off.

Make a free Mochi account, the gun and grenades are worth it.

Major tips:

1. Your health refills EVERY LEVEL, so don't get caught in a corner, run THROUGH them to a better position if you need too.

2. You don't NEED every gun, so just buy what you do need, the more cash on hand when you finish the more points you have.

3. Every time you upgrade the barricades, all of the broken ones are replaced instantly, so instead of running around and fixing them all, just upgrade it by 1.

4. A mouse will be of more use then a touch-pad, I'm stating that as a fact from experience, since I'm using touch-pad.

Note: These have been checked.

Edit to #5:
Even though it will no longer replace the destroyed barricades, it WILL fix all cracked ones if you upgrade.

Strike the LOWER #2, it no longer works, you can no longer run through zombies.

UPPER #2 does still work though, since you're still immune from pain from the mines still, abuse that until it's fixed.

Strike the #5 tip, that glitch has been fixed. At least it doesn't work for me anymore.

Major tips:

1. All your cash gets added onto your score as bonus points, such as if you have only 12K points, but 9K cash, then you have 21K, so the quest is beaten.

2. A proximity mine does NOT hurt you, so placing one at your feet and standing on it will be extra defense.

2. Since you can pause the game as well as go to the upgrade screen at the same time, how about running straight into the swarm, and buying one, it would kill most of them off instantly, if it's not enough, well guess what, you can do it AGAIN if you need too. After all, the only reason you should have to do this, would be if you are late in the game and need to knock out a mass of them coming at you together.

3. Your health refills EVERY LEVEL, so don't get caught in a corner, run THROUGH them to a better spot. You could even place mines when you go through them.

4. You don't NEED every gun, so just buy what you do need, the more cash on hand when you finish the more points you have.

5. Every time you upgrade the barricades, all of the broken ones are replaced instantly, so instead of running around and fixing them all, just upgrade it by 1.

6. You DO NOT need fully upgraded barricades to win this game.

7. A mouse will be of more use then a touch-pad, I'm stating that as a fact from experience, since I'm using touch-pad.