It’s a joke to try to remedy the situation after a desperate situation, isn’t it?

mend the fence [wáng yáng bǔ láo]

Basic meaning

Fugang: escape, lost; prison: a pen for livestock. It is not too late to repair the sheepfold after the sheep have escaped. It is a metaphor that after something goes wrong, finding a way to remedy it can prevent further losses.

Source

"Warring States Policy·Chu Policy Four": "It is not too late to look after the dog when you see the rabbit; it is not too late to repair the dead sheep."