I'm assuming then, that the land directly outside your garage, which your neighbour's gate opens onto, is public land .... in which case, I don't think there's much you can do apart from take care when exiting your garage.
Have you looked into buying the small piece of land directly outside your garage ..... I'm assuming your garage is slightly set back, so there's a plot of land between your garage and the pavement??
In fact ..... just thinking about it - have you checked to see who owns the land .... maybe it is your's after all ??
Does your neighbour's garden run right up to the pavement?? If so, you may also own the land right up to the pavement - worth a check??