Their camps on public land are illegal, but they know how to play the system. So they set up and stay, safe in the knowledge that it will take councils money and time to get them evicted.
When the legal paperwork is finally produced, they leave and simply move to another patch of ground where the whole process starts again.
Then there's the additional cost to councils of building defences such as bunds and swales to try to keep travellers off parks and sports grounds in the first place. But often travellers regard it as a challenge and find a way around them - or over them.
We report today how about a dozen caravans appeared on Southsea Common on Tuesday evening despite measures designed to keep them out.
The travellers don't seem to care that their selfish actions can impact on the local community.
At Cams Alders Recreation Ground, a group of 12 vehicles stormed the site on Friday, forcing the postponement of children’s football matches over the weekend.
Then there is the issue of the mess left behind and damage caused. At Mengham Park in Hayling Island dozens of saplings planted for the Queen's Platinum Jubilee have been trampled and driven over. Supporting canes have been put on a bonfire.
It seems wrong that this is allowed to happen. So we support council chiefs who are demanding that police use what powers they have to act when offences are committed and that the government does more to help speed up the process of local authorities going to court to tackle illegal encampments.
Because right now in this annual game of cat and mouse, the odds are stacked in favour of the mouse.