Burying a trampoline allows the surface to be flush with the ground. This makes the trampoline more accessible for smaller children, and prevents injuries caused by children falling off. Depending on the size of the trampoline, common garden implements can be used to dig the hole, and to create a soft area around the trampoline in case the children land on it. If your trampoline is a large one, then it may require a greater effort, although the process is no more complicated.
Measure your trampoline, and find the depth and the width of the hole you will need to dig. It is best to add two feet to the width to allow for fitting the trampoline in the hole, although the depth should be the same as that of the trampoline. If you dig the hole too deep, then there will be a dangerous 'lip' of earth around the sides of the trampoline.
Draw out the hole using garden tape. Stake out the area you will need to dig, since it is important that the hole you have dug is the same shape as the trampoline. Be sure to leave two feet extra on the width to allow for easy fitting. Your hole should be in an area of grass away from tree stumps, walls, or anything that will cause injury. Furthermore, if your soil has problems with drainage, place it on higher ground to avoid the hole filling with water.
Dig the hole, either by hand or with the mechanical digger. Make sure that there is a slight taper in the sides of the hole so that it is less vulnerable to collapse. The taper should be in the wall of the hole, making the ground level portion of the hole wider than the base. This will prevent the walls from collapsing, and will promote the growth of plants to bind the soil together. Save the soil you have excavated, since some of this will be needed to fill in the space left after fitting the trampoline.
Place the trampoline into the hole. If it is too big, then you will need to extend the sides of the hole. Don't worry if the hole is slightly too big, since you can always put some of the soil back in. When the trampoline is in, put some of the soil around the edge to make sure there is no gap between ground and trampoline.
Plant grass seeds or lay turf around the trampoline if you do not have grass there already. A soft surface is imperative to prevent children from hurting themselves when they bounce off. It may be best to wait for the grass seeds to take before allowing the children to run around on it, since this will inhibit the growth.
Clean the dirt off the trampoline, and be sure that it is all fitted correctly. Check that it doesn't slide around inside the hole, and that is soft ground around the outside of the trampoline. Now it is ready for use.