[jester]

Here are some ways,

1.) Elevated platforms like tree stands every 300m with marksmen with scoped rifles to snipe anyone who enters.

2.) Location, if its in a box canyon, a isthmus or similiar area you only have 1 real direction to worry about.

3.) Trenches or a moat, also used for irrigation, but it makes a decent vbarrier to intruders, couple with trip flares, punji sticks or even tincans on wire to alert you of an intruder where the marksmen mentioned above can zero in.

4.) Make it required everyone has their own home garden. Say everyone has a garden in their freind and backyards for vegetables that produce a high yeild.

5.) Put your larger field inside the town, with the dwellers homes forming a wall or ring around your main field, and they also include the mandatory personal garden of high yeild crops.

6.) Small bunkers two men, semi raised at key terrain areas to observe the aproach routes to the dfields. Remember, most fields are flat and open so, they also make a very nice kill zone.

7.) Cover the fields with machineguns, and the above mentioned marksmen to deal with tresspassers. Again, its open ground and who is going to be able to cross 100, 200 or 300 or more meters of open ground covered by machinegun fire and riflemen and survive?