Alive and Planting Achievement
Alive and Planting25
Survive 40 waves of pure zombie ferocity
This will take the most time to complete. You will first need to unlock Survival Endless which is done by doing all the other survival challenges first. Once you do this you will need to last till wave 40.
The video below shows someone getting to flag 76+ Just watch it carefully and follow the same principles and it hopefully should take too long to complete.
Just to note you need to die once you have 40+ flags for the achievement to unlock.
Also If you dont want to use cob cannons, for whatever reason, you can try this setup. Just remember to use Spikerock for all the zombonis. Thanks to Brambledamble for this setup.