My dad's just had a brainwave, how about a disused warehouse? You'd be just as likely to find an old warehouse as a field, and the warehouse wouldn't have as much noise pollution to the local area. Just have a small open door in a corner or something and a couple of fans in the roof to take out the fumes etc.. Fill it with mud, get a mini jcb in, and off you go!
Also mate, whats this nepba you speak of??