Hi rjones35:
I have been venturing on my own for mini-tours since I was 17. I am 26 now, and I have had something stolen once, and I am pretty sure it was someone I knew and not a passerby.
I am a girl rider, and pretty slender, so I always have to be cautious. Here is some of the things I learned to practice over the years. They are common sense, but still I like to remind myself once in a while.
1.
Observe, observe, observe. Some cyclists sort off get into this trance and forget to pay attention. There are a lot of unpleasant incidents you can avoid by just observing your surroundings.
2.
Don't make it easy. Cables and locks are only good against a casual theft, not that I am saying they are pointless. But if someone is determined to rob you, they will watch you and will have tools. Or, they will take your whole bike. So observing comes in handy here. Fortunately, we cyclists either tow things which usefulness other people cannot easily judge; or, they are bulky and difficult to transport on-foot. So my strategy is to remove or hide all small easily removable and identifiable things like pumps, tools, chargers, handlebar mounts, etc.
3.
If you cannot watch it, just hide it. It is rare when no one is around if you want to go site seeing in a touristy location. I usually secure my bike near an entrance to a market, information booth, or a ranger's station. That way, the would-be-thief assumes that I am inside and can see my bike. On some rare occasions when there was no one and nothing around, I just hid my bike. If it is not visible, nobody is going to go look for it.
4.
Never ever flash your wallet or show your money. Get a bicycle wallet that goes around your neck. Keep only limited supply of cash, ID, and a credit/debit card in it.
5.
Don't be afraid to make some noise. My rule is, if you think something is off, it is definitely off. Scream, make noise, be rude and obnoxious if you have to - you can always apologize later, but you will likely discourage anyone whose interest in your bike goes beyond just simple or admiration curiosity.
What I am going to say next is kind of sad - and perhaps many will disagree with me - but mostly we get our things stolen by those who have use for them - fellow cyclists.
The good news is that most cyclists are decent helpful people that you would enjoy meeting on your tours. So just observe and be vigilant, and you and your staff will be fine.
Happy Riding!
Lexie