I grew up in the Catskills. The rock wall dam may be familiar. Looks like a area where I got my ass shot full of rock salt by an angry farmer. Do you remember the name of this area or any nearby towns or roads?
Ya'll might want to employ a "brake" instead of a gag. It is made of metal, leather, or plastic and is inserted into the mouth where it fits over tongue [about 4" depth]. It presses tongue down and keeps it down restricting victim to moaning and mewing sounds. A stop, shaped like full lips keeps it from going in too far, fits over the lips looking fine. Straps attached to corners of the lips go behind the head and tie there to keep device in place. Earliest usage was Roman with extensive use during medieval torture in witch trials and other similar activities where confession was required with causing affront to ears of onlooking judges and high churchmen.