I have the benefit of living on young sea clay salty and soft and a very good HF ground.

For a safety ground you need to go deep, depending on how deep the first layer of permanent groundwater table is, ask a electrician in your town, they know, have it megged after you put it in place..
If your underground is rocky, putting in copper in trenches as deep as it will go, but then plenty of it...


For H.F ground you can put radials over , on, or in the ground.
Try ON4UN book, low band dxing ;)
I just buried 1800 feet of copper wire in the ground, laying on the ground and some wires are 6 feet up running over the fence.

That all for the 160 meter vertical L antenna....
I have 17 extra copper 7 feet and 10 feet long copper pipes driven in the ground on strategic points which are connected to the HF ground grid.
When the ground is hard, use copper pipe, hammer one end almost close put the water hose to the other end, and slowly with the water stream on,
push the narrow end with the waterjet in the ground.
dig up a 1 foot by 1 foot and 1 foot deep hole before you do that, after the rod is in place use bentonite or rock salt to fill the hole, both will spend salt along the rod for years to come, and improve the ground.

After 4 - 5 years replenish the bentonite or rock salt, bentonite can be found in some cat litter material, look on the bag, it will give the material it is made off.
Rock salt i get here for agricultural shops, used as licking stones for cattle.

Hope that helps...