Advice needed regarding outdoor litter training

Hi

I have two lovely neutered and spayed bunnies who are mostly very well trained with their litter box when they are inside their secured hutch-and-run which is outside on the patio.

Every evening I let them out to run round the garden, and they poo EVERYWHERE. Its very hard to collect it all so it looks a right mess, but they really enjoy their free running and I don't want to stop them having this play time. They also come in the house and they don't poo in there, however they are only allowed inside for fairly short periods so that could be why....

Does anyone have any tips to get them to go back to their litter box to poop while they are free? They do go back in and out of the hutch because I leave the door open.

(In advance; yes my garden is VERY well secured from predators and I remain with them while they are loose to keep an eye on them.)

I used to have to vacuum my lawn before the guy came to mow it!
Nothing better (for a rabbit) than running round the garden pooing everywhere. Sorry can't offer any advice ... but it is very good for the garden (including lawn).