The more I think about this the more I realize that this is a good weekend project, And it's true that saving $600 is the same as earning $600, and yes, I'd would manual labor for $300 a day, and it won't take me a full 2 days.
Part 1) So here's my thoughts. Based on the last time I had it done I really don't think he trenched to 1 foot(edit, I now read it's only 6-8 inches - but it 10 inches better)? Also, did a terrible job of getting the gravel back, mixing the soil with the gravel when filling it is and wasn't thrilled with his finished grading. So I was thinking that even if i did pay to have it done I was going to pull the gravel back myself - further than they would. So as long as I'm doing that, I can get some tarp down to put my soil on as I trench, then just roll it back in.
Am I over simplifying it, or is that really all there is, as well as needing to treat the soil I pull out.
Part 2) I need about 68 mixed gallons of Termidor to fill 170 linear feet. Do I just mix it in a big garbage can? Then what would be the easiest way to then fill the trench? Or just mix 4 gallons at a time and trench one 10 foot section at a time then back fill. Again, am I over simplifying it or is this really all there is to get the same results as the pro's. Especially since their not drilling due to post tension including the patio and porch which was poured as one.
3) Can I use a higher concentration of product or is there no increased benefit? I've got 170 feet