You really need to find/create/build/borrow a smaller area to work with him and please don't use sedatives on a horse you are planning to train or ride. Not only will they not learn with sedatives on board, but they can be even more unpredicatably dangerous because most sedatives have an "excitement threshhold" which once the horse exceeds, can cause the sedative to work in the exact opposite way you want it to - making them worse off. Not to mention that if the only thing keeping you safe is a sedative, there's no way to predict exactly when it will lose its affect and leave you hanging.
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PH Cody
HorseHobbyist Site Coordinator