OK. I've really been through it all. I take Propecia, Minoxidil, Spironolactone, and use Nizoral shampoo. I've also had a $5,000 hair transplant. As you might be able to tell, I don't take losing my hair lightly.
It's good to see that you're taking test. This is the easiest to combat with simply Propecia or Proscar (same thing, different doseage). This is because as other people have mentioned, the 5AR enzyme. Proscar will stop the DHT conversion. What I do is stay on the four I mentioned above year round. When I do a cycle, I switch the Propecia to Proscar to get the additional 4mg of finasteride.
If you stick to test, you should be fine, but unfortunately, it doesn't make for the best cycle. If you add Deca it can get very tricky because Deca converts to a less hair toxic metabolite in the scalp. This conversion is catalyzed by an enzyme which is inhibited by Propecia/Proscar, so taking Propecia actually INCREASES Deca's hair toxicity. If you're going to go on Deca, you should go off of the finasteride.
Regarding the AAS that are already DHT derivatives (winstrol, primo, etc.), finasteride won't do any good, but it won't hurt. This is where spironolactone and nizoral shampoo comes in. Use these and you've covered your bases.
Remember, once you go on finasteride, you don't ever want to go off. Your hairloss will quickly catch up to where you would have been if you never used finasteride in the first place.