Sorry your thread got hijacked by the buddy nazis.
My first dive after cert was also solo. It didn't go as planned, but I was safe enough. I don't regret it. About half of all my diving since cert has been solo. I spent a lot of time and money getting into it and I'm going diving! I try to get folks to go all the time. I have learned a lot from really good divers (thanks to the crew of the MV Spree!). I prefer a buddy because it's easier and we can split expenses, and it may be safer depending on who it is. So don't sweat the preachers. I suggest spearboard if you want to get away from the light weight "spearos" here.
As for your question, though, I think most anything you see you can copy. I carry a short cord with a spike on one end and a clip on the other. The spike goes through the fish, anywhere you decide really, and then back to the clip. Wildlife generally won't bother you about your catch as long as you're in control of it. I've lost many more fish to cudas than sharks, but either way they will take it when you spear it and while the fish is freaking out. Once you get control of it the other predators will watch (you can see the jealousy in their sad eyes).
I especially don't like the idea of hanging them on a long line away from you. You're attached to something that absolutely will invite a shark to grab it. In addition, the fewer long lines in the water with you the better. When rig diving some guys will tie the stringer off to the rig. Something may grab it but at least you're not attached.
You can also carry a catch bag. They are very popular in FL, especially with lobstering. I never liked them, but when I lived there, everyone had them.
Sharks, over time, may become aggressive about your stringer. The good news is that they will do so progressively and when they start you should leave the water. I find triggerfish more danger than sharks, and they are yummy too.
Good luck and happy hunting.