I have plenty of chewing rodents at my farm. They have breached my drip irrigation lines on several occasions.

If you don't see any burrows, then there is a small chance they chewed on the line while it was in your shed, or laid out on the ground before you buried it. Only when the line became a little more brittle with age did the thinned "bite scoops" finally began to leak.

Of all of the wildlife at my farm, the chewing rodents and the digging armadillos are the only ones that have pi$$ed me off.