I want to place two tennis pole sockets into the ground in my garden. A picture depicting what I am thinking is provided.

It is so that I can place to upright wooden poles to hook a hammock in between and remove the uprights when not in use leaving the sockets in the ground out of sight.

The socket can be viewed here http://www.hexasports.co.uk/product.asp?productid=9

Will concreting like this spoil the grass above it?

Is the concrete even necessary and going to secure the upright? Or could 15" of socket be secured in ground as is?

Thanks.

I would say that the hammock hooks would be aprx 1300mm from the floor. So max 2000mm of timber.