Memento CAN be used as a relational database. The relational way to do this would be to use two libraries: Sites (or whatever) and Inspections. Sites would include info about each site, and Inspections would include at least the date of inspection and possibly other info, like inspector, findings, etc. To implement this, you'd define a one-to-many link to entry field in Inspections to identify the site that was inspected.
Memento has other capabilities, though, and one of them is many-to-many relationships. It's not relational, but instead of a link field in Inspections, you could define a many-to-many link to entry field called Inspections in the Sites library to the Inspections library.