My father is having a similar problem. I found a link to a website that offers a "bib lock". The only drag about it would be that you would have to screw and unscrew the hose each time you need to water. http://www.plumbingsupply.com/hosebibblocks.html
I was also told that there is a lock that you don't have to keep unscrewing all the time. Supposedly you hook this "lock" up to your faucet and the hose screws into that. Then you control the water flow by getting an allen wrench and screwing this mechanism to allow water flow. I guess that bad thing about that is if they really want your water, then it's only an allen wrench away...