Long outside wire run - can I JUST ground at both ends?
The National Electrical Code, that is the controlling document is most locations of the US, requires a 4 wire connection between a main and sub panel now.

That is; the two hot legs, the neutral, and a grounding wire. The ground wire can be a separate wire from the other wires but should be run in the same trench with them.

You still have to establish a ground at the separate building using one of the Code approved methods for a grounding electrode. Such as the one you cite in your question.

There are many questions here on SE that address this issue.

Good luck!