If you have been protected for 2 years without incident, they you know how effective these fences can be.
As for troubleshooting, the concepts are pretty simple. A working functional charger sends an electric pulse down the line on the hot side. If there is no path to ground to complete the circuit, nothing happens. The fencer cycles and hits it again. That goes on pretty much forever. So what can go wrong?
First, is the fencer working? To troubleshoot that, disconnect the fence and test the charge right at the fencer level. Hot or not? If not, is it properly grounded? No loose wires, etc? If all seems to be correct and you can't get a charge to jump from the ground connection on the fencer to the hot connection on the fencer, then the fault lies with the fencer. If solar, does it have a good line of sight to the sun? Not shaded, etc. If all seems to be working, then the fencer might be bad. That could be anything......bad battery, damaged solar panel, bad fencer electronics, etc.
If the charge is hot from connection to connection, but not from the ground to connection, then the connection to ground (literally the ground you stand on) is faulty and needs your attention. Dry soil? Bad connection?
If it is hot there, but doesn't stay hot, then it may be grounding out. Weeds, bad insulators, or some type of connection to ground that is draining the battery down. So walk or work the line to found out where it is grounding out. Basically, the charge constantly goes to ground and the fencer battery is quickly drained.
If it is hot and working properly and not grounded, then the fault lies in the fence itself. Wire or tape? I have had the wires in tape fences break. A fence should be as hot at its terminal end as it is at the fencer. So start testing it at the terminal end. If hot at the beginning, but not at the end, start at the end and work back to the beginning. Eventually it will turn hot. Between where it is hot and where it is not is where the fault lies.
As for fence testers, there are a lot of options. The quick and dirty version if you have the nerve is to simply touch it. If you can do that without regret, you need a better fencer. Another option is to use an insulated tool like a plastic handled screwdriver. Put the shaft on a metal grounded object like a steel fence post, then touch the tip to the wire. A hot fence will throw a spark across the tip. Or better still, buy a fence tester. There are two versions of those.....range lights or better, one with a meter. I like the meter versions but they are much more expensive.