Outdoor Lighting Approaches
Many outdoor lighting options are pretty straightforward. Install a transformer and run the cable under a few inches of mulch or lawn. Or drill a few holes in the wall and install the wall-mounting bracket that came with the light. But extra care must be taken when dealing with more complicated applications such as inground fixtures, tree lighting, and water.
Inground Fixtures - Inground fixtures such as well lights require a bit of care to get them right. These fixtures should generally be used in places where they are likely to remain. Flagpoles, fences, and full grown trees are good candidates for an inground fixture. Shrubs, saplings, and flower beds should be avoided.
Remember when you are digging around the base of a tree that injuring the roots can severely damage the tree. You don't want to go to all that trouble only to have a well lit but dead tree in your backyard. Sticking to fixtures that are less than 12 inches deep will help you avoid this problem.
You also want to consider the problem of moisture. Inground fixtures are designed to be sturdy and robust. But even they can be overcome by excessive exposure to water. Use granular material to lay out a 3 inch drainage bed to keep your inground fixtures dry.
Tree Lighting - The density of a tree's foliage will determine how you light it. For trees with very dense foliage, like pines and firs, there isn't any interior to illuminate. Position the fixtures away from the base and aimed toward the top. Lit from behind, these trees can be silhouetted to stunning effect.
Other trees, such as oaks and maples, may have dense foliage but interesting bark or elaborate branch structures that are visible from underneath. Place lamps at the outer edges to focus light into the branching and on the trunk beneath. These trees are ideal candidates for "moonlighting," placing lights within the branches as well.
Trees such as birches and walnuts have more open canopies. Shine light up into these canopies from underneath. Or light them from behind so that the shadow falls on a wall.
Flowering trees such as dogwood and fruit trees should have their edges and tops lit up to show off the flowers or fruit.
Underwater - For underwater lighting you want a composite molded fixture with a watertight seal around the lens. The materials should be rated for underwater use. Copper and brass will oxidize over time, harming underwater plants and animals, and creating an electrical hazard as well. Sturdy aluminum is a better bet.