Thanks for the input guys. Wow Martin, my light pollution problem suddenly seems insignificant compared to yours.
I should add that the house has only recently been completed and is still empty yet. It is on the market if anybody has a lazy $1.6m. Maybe you could buy it and remove the light for me.
My garden is quite small so there is not a lot of options for trees/hedges behind the observatory. I'll probably resort to something like Martin has done with a screen that can be quickly put up and taken down.
I'm more of a galaxy guy than a nebula guy. I was under the impression that narrow band filters, like the Optolong L-Enhance, were only really good for nebulae. It would cut out most of the signal from the galaxy blowing out the acquisition times. What narrow band filters do you use, Martin?