Most subsurface drains are constructed by excavating a trench, installing a tile, and backfilling the trench. Control of the machines to assure proper slope of the drain has been a major problem, but recent development in excavation technology, including the use of laser beams for grade control, have helped to solve it. Traditionally, clay or concrete tile has been the principal material used, but many types of perforated plastic tubes are now employed. An advantage is the reduction in weight of the material handled. With proper maintenance, drainage systems give relatively long life. Selected herbicides are often applied to keep woody growth and water weeds out of the channels. Grates are usually installed over outlets to prevent rodents and burrowing animals from building nests. Surface drainage systems need almost yearly maintenance to assure the slope and cross section of the channels and the slope of the graded areas because the slopes are so flat that small changes in the ground surface can make marked changes in the ability of a system to function. Subsurface systems need periodic inspection but usually require little servicing. The outlet of the system and infrequent structural failure of the material are the usual points for service.