Below the old octagonal blockhouse on Davis Island the Sheepscot slides past, brown-green and quick, and Edgecomb spends its summer half in the woods and half in the water. Nervous Ticks mows the in-between lawns — the ones that run from a shady stand of oak down toward a slope of tidal grass. The round covers trimming, edging and clearing the beds, along with the fall raking when the leaves come down all at once. A yard cut evenly, with sharp borders against fern and ledge, holds its own against woods that would happily take it back. When spring loosens the ground, the cleanup starts the whole cycle over again.