Securing a gate so it does not open

[john9159]

Hi,
I manage an allotment site where one member (getting on a bit in years) insists on driving on another persons plot with his car.
What I urgently need to do somehow stop one of the two gates to the site from opening.
The gate has a riser bar on one side which goes into the ground holding the gate secure. Ideally I want to somehow fit a lock to this but cannot for the life of me comeup with a solution.
I thought of drilling through the side of the gate but as the metal is 1/2" thick, this will take too long to do.
An alternative was to drill through the riser bar and fit a padlock through, which would stop the bar from being raised and hence stop the gate from opening on one side.
I need a quick solution before he gets back from holiday and causes more havoc.

Thanks

Sorry I can't upload an image from my documents, I don't have a url for it.

[welsh brickie]

drill and fix a steel eyelet to the concrete on the floor by the riser bar and chain it to the gate,