Moist ground is fertile breeding area for buttercups so one answer is to raise the level of the soil by building raised beds or just adding topsoil on top of areas where you wish to plant a lawn. Adding Super Sweet lime to your soil twice a year will make the soil less acid and buttercup loves an acid soil so this will slow it down. Consider a natural woodland landscape of pathways through the trees. The pathways could be of cedar shavings contained between rocks or timbers. The beds would be raised beds around the base of the tall trees planted with woodland trees and shrubs such as Japanese maples, rhododendrons, ferns, pulmonaria, bleeding heart, and groundcovers. There is a show garden in your area called The Chase Garden that you can visit for inspiration. Keep growing, Marianne Binetti