Mis-treated deck help

1. Missouri
2. Full Sun
3. not sure what Type of Wood - see picture
4. no Mold or Mildew Issues
5. Main Issues with Previous Stains - looked bad after a year or less...seemed superficial (i.e. dog scratches exposed plain wood

Sometime from late 2012 (after October) to July of 2014 we partially stained the deck (horizontal surfaces) but never finished the uprights. We moved into our house and the deck had never been stained. Didn't document well.

June 2016: I power washed, prepped and stained according to Defy local retailer and applied Defy water based stain. See picture of after prep and after staining.

By May 2017 it didn't look too great (see picture)

So it's been almost 4 years. I'm putting a cover over the deck and want to make it looks good. The picture through the window with only 2 chairs on the deck is what it looks like today. It's been raining on and off.

I will need to replace a few boards.

I want something that will last long / low maintenance.