Lower grass and beds shows how the Olive tree has grown.

I don't think they will hide fencing very well as they are fairly open trees. Nevertheless, it good to see it has grown well in the 3 years since you planted it out!

Have you seen any olives on it yet? I ask because they are wind pollinated & therefore you need a few quite close to each other if you ever expect to see them.

Have you seen how they grow them commercially in the Mediterranean countries? They plant them quite close together in big fields, rather like orchards for apples.