I went on a hike with my wife the other day in Norcal. This place had a creek that led into a cave that you can swim in. We both left our backpacks at the cave entrance and then swam through it to the other side to explore, trusting that no one would steal our stuff. All the while though we were worrying some about our back packs which had our money, keys and phone. But our stuff was ok and all there when we got back.
What can we do to keep our backpack safe the next time and so we don't worry as much when we have to leave it for a while?
I did a search online but wasn't completely satisfied. I was hoping there was some type of deterrent device you can set inside your backpack so when its moved a loud alarm goes off. Is there such a thing? The other thought was taking money keys and phone with us but in this particular situation even if we carry a waterproof fanny pack there is still the danger of it falling and/or getting lost, especially in a partly dark cave. Any suggestions?
We are newbies to Outdoor activities like these.