We had the same problem until we planted a load of wooden cocktail sticks in the areas that the cats tried to hide. (Make sure they're wooden - plastic ones will a) look rubbish & b) never rot. Only thing is you'll have to top up your cocktail-stick patch occasionally.)
Don't worry - they don't hurt the cats, they simply avoid that area. It's never stopped the cats coming into our garden completely but now they're forced out into the open where the birds can easily see them. We've not had one feathered fatality since.
Word of caution though - DO NOT use this solution if you are likely to ever have young children playing in the garden. While cats are smart enough to avoid the area, if a child fell on sharp cocktail sticks it would be very painful.