It can be quite embarrassing to see your cats squeezing through the fence to use the neighbour’s garden as a toilet when you have provided a perfectly good litter tray at home. It seems, however, that there is not much you can do about their behaviour. According to this article cats choose to use the neighbours garden because they are marking the edges of their territory. The behavioural trait was discovered when GPS trackers were fitted to nine cats over a period of eight days. 150 hours of camera footage were caught and 3,000 owners were also surveyed. Town cats have to spend the greater proportion of their day protecting their territory against rivals and half of cats had to deal with other cats entering their homes to steal food. One way to stop your cats using your neighbours garden could be to leave areas of loose soil on the edges of the garden to encourage them to use that instead.