Why would anyone choose to bury cable.  One reason is that burying cable protects it from storm damage and has lower maintenance costs than aerial cable installations. In addition, aerial installations often lack aesthetic appeal.
Draw backs to Direct Burial Cable:

•    Direct burial cable is expensive and must be made of a non-contaminating high-density polyethylene material.
•    Degradation of signal strength is possible.
•    Damage from animals is possible.
•    Direct burial cable needs to be installed to a depth of 24” underground.
•    The cable should be laid on 4” of sand.
•    Pressure-treated board on top of the cable should be applied to provide protection when back filling.

In general, the above method is not very user friendly.

Recommendations from Omega for burying cable utilizing Flexible Cable Conduit

Omega Part #  54014355 (1/2"- 30.5m) or 54014134 (1"- 30.5m)

•    Insert all cables inside the flexible underground cable conduit, available in 1" and 1/2" diameters.  (To aid in feeding the cable, a vacuum cleaner may be used to draw 2 pieces of string (preferably nylon) down the conduit. Attach 1 string  to the wire and pull the wire back thought the conduit.  The second "pull string" may be left inside the conduit in case you want to run more cable.)
•    Dig a small 4"- 6" deep trench and lay in the conduit.
•    Ensure that each end of the conduit (pipe) is sealed with silicone.
•    Replace the dirt to cover the conduit.

This method of burying cable will ensure the longest cable life possible in an underground installation using standard readily available RG6 coaxial, Cat5e or speaker wire.

The conduit will protect the cable from moisture or from digging animals. It is also easier to replace cable that has failed without digging up the area again once the conduit is in place using the second "pull string" left inside . Flexible conduit is also strong enough to protect the cable from expansion and contraction of the earth during freezing and thawing.