Posted: 10/09/2014 at 14:23
Marbeck, I'd dig out a border, about a foot wide, and plant a variety of low growing shrubs. Often people take short cuts when there is no barrier in place, even a low barrier of shrubs gives the trespasser fewer options. The shrubs needn't be thorny or large, a low set of shrubs makes a psychological difference when viewed by the human eye.
Buying now at your local Garden Centre or DIY stores shouldn't be expensive. When choosing look for shrubs that get to 2 -3ft tall with the same spread. Even just planting the very front of the lawn will have an effect. It's a natural instinct to avoid a barrier however small so it probably won't cost the earth either as there are plenty of bargains to be had at this time of year.