Wait until night fall and cause havoc.

Big boy has an idea. What if they let the Mirelurks out of their pens and caused havoc in the town. The guards would be distracted and probably would leave their posts to help. They would still have to ford the river but if it was shallow enough for Mirelurks to be nesting it shouldn't be a problem for an 8ft or 7ft tall mutant to cross. If they do it at night darkness should cover their approach. If Big boy's feeling particularly ballsy they might be able to avoid crossing at all and he can try and shoot the lock off the gate with his hunting rifle and free one remotely.

He informs Biter of his plan and the two of them wait for night fall.