I have a leylandii hedge that is too tall. Is it safe to reduce the height by 18 inches or so? I live in a rental property and can't mess about too much. The hedge is about 10 feet high facing the house and about 8 feet high facing the road ( I live on a hill and our garden is below street level.
I am not quite sure what you mean by is it safe?
You won't harm the hedge if you cut it-but if you go into brown wood it will not grow out again-it may look a bit unsightly
You can trim it with no problems, and the top will re-grow from young growth, so the hard line will soften quickly.
We did this a few years ago with a conifer hedge, taking off about 6'. It helps to use large loppers or a pruning saw if needs be to cut the stems at a diagonal facing down and inwards so they are less visible. As long as there is green growth left at the outer edges of the hedge it will regrow and cover up the cut stems and be easier to keep trimmed with normal hedgecutters.