Richmond Park = Full of tossers

At least High-vis for the deer

They tried this with ponies in the New Forest.

The number of pony deaths, as I understand it, increased - People (drivers, specifically) began looking out for hi-viz ponies.

Because not all ponies wore hi-viz, and the hi-viz wasn't viz if the pony was facing away, and because people were no longer looking out for the ponies themselves (or compensating in some other way), it became ponysquish time.