Another tip: if the ground is undulating, allow the mower to follow the countours of the ground when you are making the shape - this is hard to describe in words. It means not being rigid about where you want the outline of your shape to be, but going with the lie of the land, allowing the mower to lead you ...the end result will look very natural, which is how you want a wild garden to look, rather than imposed and contrived. Believe me this works, and when you get the hang of it, it's a lovely, very creative thing to do, and you can alter the shape between one cut and the next if you don't get it quite right the first time. Fun with a lawnmower - who'd have thought it!