It's probably cheaper, to let the visitors pile up until they're flush with the adjacent surface :-)
Didn't the carpenter ask you any questions about PTL (pressure treated lumber) ?
Plain pine, rots like a bastard. Been there, bought the Tshirt. Current backyard project, is built completely out of PTL, with a hybrid redwood-coloured finish on the outside.
If you must use plain pine, at least use fasteners from the back of it. Don't nail into the front surface, because pine rot starts right around where the nail goes into the top surface of the board. No, it is not physically possible, to make an airtight seal around a nail-set.
Sure, lay on your oil. Go to it. But that's not as effective as a chemical which is sucked into the wood via an applied vacuum. PTL comes in different grades, and the grade intended for below-grouns usage, has the highest amount of chemicals sucked into it. It takes multiple vacuum runs, to get a good percentage of coverage through the volume of the wood grain.
Whatever oil the guys tell you to use, you'll be applying it once a year. Until the deck rots out, of course. Oil can certainly cover surfaces. Most of the surface, will have some protection. It's the fastener holes I consider to be "a hopeless situation". That's how the rot gets in.
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