This is primarily because you are using one dropbox across multiple clients. Technically each client should have their own account, but then you couldn't easily access it. With our solution, you could buy an account for each client (but charge them a reimbursement fee, and probably mark it up some). You would have the ability to make it read only. Also, the system stores unlimited versions, so if a customer did accidentally overwrite the file, you can restore a prior version. You would also know who overwrote it, when and at what date/time.
Wayne, in your case, why not just not install dropbox at the client, and instead use the web client to pull down the files when you need them when you are there?