Sorry to hear your bad luck w/ knot failures.
A few suggestions for you that I agree w/ others on here.
1) Go to the Orvis podcast. They review knots in detail on one of them. He says the simple clinch knot was proven head to head to acheive a higher tensile strength than even the double clinch and many others. They used a fancy strain gauge to measure breaking strengths for differnet knots. It's (clinch knot) a tried and true knot, and if you're using the right tippet and procedure, it's a more than suitable knot over most others for steelies.
2) Spit on your line before you cinch it tight.
3) I' ve used Seagar products and they're not as advertised in my experience. Maxima, Frogg Hair, and Drennan fluorocarbons are tops on the ole' silverbacks list. I tried Drennan a couple of years ago, and I'm sold. Strongest stuff I've ever used. It's a little larger in diameter than comparable line sizes, but that means if you normally use 10 #, use an 8 # Drennan. It apparently doesn't deteriorate over time like mono does, but I say buy new spools each and every year. The only down side, is it's really hard to find. I get it in NY, but can be bought on Ebay. Don't try to save a few bucks on a critical component for your rig.
4) +1 on the rusty hooks, if you got your flies wet, the eyes may be crudded up and may be cutting your line.
Hope this helps. Good luck!