Landscape lighting...the scene of much heartbreak!
Here is what works for me, as well as what hasn't worked very well.
Mounting the light is a real challenge; simply letting the conduit support it isn't enough. I will pound angle iron, or additional support pipes, a foot or two into the ground. Very often, I have the fixture mounted on a frame that is attached in turn to these supports. If I knew I was going to mount several lights, I might pre-fab a small concrete pad with the braces in it, and bury the pad.
Pipe is essential; I use PVC. UF cannot be re-pulled, or repaired without digging. I hate digging; I try to do it just once.
How deep? Code aside, you want the pipe to be at least a little more than one shovel blade deep, and below any lawn sprinkler piping. You want the gardner to miss hitting it when he goes to fix his lines.
Bell boxes are not satisfactory where they are in direct contact with the ground, or poured into concrete. They simply corrode away too fast. The same applies to buried extension cords?
Splices and connections are made in covered plastic (or Fiberglass) cylinders, open at the bottom. These are about 9" diameter, and a 18" long. You drill holes in their sides, or enter them from below; there is no connector or fitting used. Your wires are connected in the box with ordinary wire nits, then the entire nut is dipped in "Scotch-Kote." This gooey brown liquid is thinner than "Liquid Electric Tape," and costs about $1 per fluid ounce.
Landscape design can often lead to confusing layouts, so you should also pay extra attention to identifying circuits, breakers, and the location of controls. It is not unusual for the photocell to be located three buildings over! Likewise, receptacles should be identified as to any timers or photocells that may control them; several times the receptacle the gardner wanted to use was "on" only at night, as it was intended for the Christmas lighting!
Speaking of photocells: when you use them, especially when there is a contactor for controlling several circuits, it is worth your time to install a bypass switch in an accessible place, so the circuits can be easily tested.
