The area and the way you approach a potential shelter location is critical in your well being. As you can see in the video the shelter location and stability were acceptable, although the apparent danger of the occupants (rattle snake) were not.
This mine shaft would have been a suitable shelter, but it is being visited by too many dangerous animals. I noticed coyote and cougar tracks around the entrance to the mine and faint cougar tracks within the mine. Not something I want to run into during the night when I am trying to sleep.
The snake would have made a suitable protein meal in a survival situation. If I had been in survival mode and been traveling for a couple of days, I would have taken the chance of killing the snake and using the shelter for at least one night.
I would have made a good fire near the entrance to the mine, ensuring that the smoke positioning would not be a problem. I would also have adequate protection at the entrance by placing a wall of thorny bushes to deter anything trying to get in. I would also have several long spears on hand in case I had to fight something off.
Usually a good fire will keep most larger prey away. It is important that you do not box yourself inside and make sure you have a quick way out if needed.
It is important to know that some mines may have undetectable gases coming from them that can kill you. Usually, these types of mines would be labeled or sealed in some way, but not always. Mines can be found a hundred miles from civilization, so finding one may not mean you are close to being rescued. Pacing yourself and conserving energy is a must.
When selecting natural caves and overhangs, it is very important that you check the walls and roof for stability. Some stone will crack and slabs will fall loose when heated by a fire, especially when it is frozen. If this is happening you will see slabs of rock on the ground under the overhangs or inside the caves. A good indicator of where not to sleep.
Always check the cracks and holes in the caves or bushes for possible dangers of poisonous critters. Holes can be plugged with heavy stones if they appear deep or long and you can not see inside them.
Some caves will have bats as identified by the strong urine or ammonia smell coming from them. Gases produced by bat guano can kill you. Some caves may have large bee hives. The honey is not worth what the bees will do to you if you are not wearing protective clothing. Some caves will have both bees and bats. I know this from first hand experience.
When sleeping under trees make sure the branches are sturdy. Remember that in a lighting storm, trees act as lighting rods.
Never put a shelter in a dry river bed. Need I say more on river beds? Never sleep near the banks of rivers or lakes. Large animals, especially bear, like to drink from them. Moose, when they are in mating season, can get very agitated and will attack at a moments notice. If you are in crocodile country and sleeping near the banks, you may be whats on the menu. These large monsters can be found up to 100 yards or more from the water.
Common sense will usually assist you in locating a suitable shelter location. Knowledge of survival shelters and thinking safety at all times will better your chances of making it out alive.
Stay Prepared! Stay Alive!