I suspect that would make little or no difference, since this would almost certainly be the reality:
It looks like you've had a decent run with the previous manager, but that's run out now, and the bottom line is there's really not a lot you can do. You talk about mounting a sign on a fence panel, which isn't on your neighbour's land...well, whose land would it be on, and would they let you put it there? Try it by all means, but I'd be surprised if you were able to get something up that would stay around for long. Looks to me like you need to start focusing your thinking elsewhere. Assuming the sign's a gonner - now what? If you'll no longer be able to rely on passing trade - which seems likely - what else can you do to get customers in? You mentioned 'customers sent to us by various fitters' - is there anything you can do to build that side of things up? Maybe ring all the fitters in yellow pages and offer them a kickback if they recommend you? Or advertising in the local paper, or in shop windows? I don't know. It just feels to me like you're trying to shore up a temporary arrangement that's run its course and in truth can't be saved, and that you'd be better off trying to take a step back and look at the thing in other ways.