Per every 1 btc you send to a unique Bitcoin address, you will in return get a pgp signed certificate with an issue date and a return date and to which bt address. I currently offer two types of contracts at 220% at 21 days, and 300% at 60 days with option to extend at a offered %.
Who's option to extend? Yours or investor?
I'm in so long as:
a) investor can refuse to extend after the duration.
b) And this is the tricky one for BTC: You can offer reasonable security against default risk. That would probably involve your not being anonymous and some sort of asset security in place in the non-anonymous non-bitcoin market.
Yes you do not have to extend your contract. This is just a perk for the person who wishes to buy more contracts. This would make a huge discount.
As to your B statement. The security is that I have a mass mining op (in the 10's of ghz) running for my own use and can cover any loss of contract I accept. I can and will deny orders that are to rich for my blood.