The previous owner of my house built a cheap wooden deck with the
cheapest pressure treated wood possible. That was maybe two years ago
and he didn't stain or paint the deck. When I stain the deck last
year, I noticed some good cracks along the grain line so I stained the
whole deck thinking it'll hold up to the elements.

This year, I notice even larger cracks and some surfaces are starting
to flak.

What should I do to preserve the deck? I am thinking of getting some
fillers and restain the deck. Do I need to seal this surface at the
end with a clear coat? I don't think so because it's outdoor. But
the stain doesn't seem to be able to seal the large cracks though.

Please help! Thank you.