I want to shoot a video flying through one of our local canyons. With mountains on both sides and a couple of slight bends I am worrying about signal loss. Any advice?

If you keep VLOS on the aircraft, unactive automatic RTH in case of lose of signal to avoid him to take the shortest path to come back

Watch out for down and up draughts - they can be quite localised and strong near the walls.

Hi, RC signal might lose if there is a big obstacle in the middle of the drone and RC, you might need to keep an eye on it. And like 2# mentioned, please also keep the Obstacle Avoidance on to fly, but noted that if there is no GPS signal or the reaction of RC signal loss is Hover, the RTH might not work.
Actually, we suggest flying in open areas. Keep flying safely.