You can prevent a claim from expiring by doing work on the claim and reporting the work to the government. To renew a placer claim for another year, you have to report about $400 worth of work per 20 hectare cell. You can count your time at $40/hr and helpers at $30/hr, and you can count some Food/Lodging and Travel costs. You and a buddy can do it in an afternoon.
There is another way to renew a placer claim - pay money to the government - $800 per cell. Nobody likes doing this, but it is good to have the option.
Another option is paying some person or company to do work on your claim. We offer this service. For the same kind of money as paying the government or less, you can generally get the Good-To Date moved out multiple years. You can also get information about your claim from the results of the work. And you might get some gold.
When you consider a claim you might buy, the Good-To Date is important. Some claims don't require any work done on them for years.