I've never seen one in the ground. At times in a grout line but not in the ground. I don't see anything in the manuals saying yes or no. It is not common practice.

What is common practice for routing the 4-wire cable? I have to route it approximately 60 ft. from the spa edge to the Easytouch 8.

1/2" electrical conduit with sweeps, not 90's. All sweeps facing the same way. In other words, do not piece things together in a way that a fish tape or wire to pull the cord will get stuck.

That's class 2 wiring. Not rated for direct burial. PVC is cheap. And it will last. Throw it through some conduit.

1 inch conduit is not much more than 1/2 inch and it makes it easier to pull the wire.

I have a two year old pool/spa with an iS4 mounted at the waterline in the spa. It is beginning to short out. My research has led me to believe that there are less problems like this when the remote is installed on the deck rather than in the spa. The installation instructions call for 1/2 or 3/4 inch conduit with gentle turns for the wire.