A mesh square three sided tunnel to secure the pipe from exterior damage (such as a fox).
We recommend always having a secure bolt hole for rabbits and guinea pigs - the Top Box or Hay hutch offer this.
Another solution is either turfing over a section of the pipe or burying a small section to trick the fox that the rabbit has gone underground.
Pegging this guard over the pipe will stop any predators from worrying the central section of pipe so the rabbit can hide in peace there. 3ft long.