In Fieldrunners (iPhone) what is a good strategy for the Marathon Challenge in Grasslands

N.O.V.A. should be saving your progress automatically, and there should be a continue option at the top of your menu the next time your game starts.

If it doesn't, your best bet is to re-install the game, as this usually seems to work for others who had the same problem.

For the iPhone version, I recommend using Marigolds on Lvl 1.1 (only the base zombie)

Basically you want to set up 3 lanes of marigolds with a single garlic at the front to divert the zombie into the other 2 lanes.

I hope this unicode art makes sense

┌─┬─┬─┬─┬─┬─┬─┬─┬─┐  
│S│M│M│M│M│M│M│M│G│ ← Z
├─┼─┼─┼─┼─┼─┼─┼─┼─┤   
│P│T│W│ │ │ │ │ │ │ ← Z 
├─┼─┼─┼─┼─┼─┼─┼─┼─┤    
│S│X│M│M│M│X│M│M│G│ ← Z
├─┼─┼─┼─┼─┼─┼─┼─┼─┤   
│P│T│W│ │ │ │ │ │ │ ← Z
├─┼─┼─┼─┼─┼─┼─┼─┼─┤   
│S│M│M│M│M│M│M│M│G│ ← Z
└─┴─┴─┴─┴─┴─┴─┴─┴─┘

Legend:

• S = Sunflower/TwinSunflower
• M = Marigold
• P = Peashooter
• G = Garlic
• X = Gold Magnet shrooms
• T = Tallnuts
• W = Spikeweeds

The idea is to slow down how you kill the zombies. So as quickly as possibly, place the garlics to direct the zombies into the two lanes that are protected. After the initial setup, it's just a matter of placing the marigolds as quickly as possibly.

EDIT: I should have said that you place the gold magnet shrooms so that you get automatic coin collection; having two means less chance of a miss.