I don't think all nodes need to agree in BTC all the time. What's more: double spends can happen because nodes disagree which transaction is valid. Only after one transaction is added to a block, and when nodes update their blockchain with that new block, it is decided which transaction was valid.
So that's why I asked (and still am asking) how you can force miners to reject a certain transaction/block that contains a transaction that was locked by the masternodes. It's the miners who are writing the history. Masternodes only "lock" transactions, but I don't understand how they can enforce that lock.

Some of my previous questions about DASH are still not answered. To make it less cluttered, I rephrased them and put them in a list:

1) How are the masternode locks enforced in the network? How do you force miners to not mine a double spent transaction?
2) Is it possible that there is a competing locked transaction? If that transaction has a higher fee (double spend attempt), I guess the miners rather confirm the transaction with the higher fee...
3) Masternodes don't get fees to lock transactions? What is the incentive to do the work? How are the masternode rewards distributed? How can the network "know" that masternodes are online and doing the work in stead of just being idle to have a lower bandwidth usage?
4) I wonder how you can have so much transactions per second? (the slide shows 500-1500) I read that bitcoin is limited to 7 transactions per second. I showed that it seems impossible to lock 350 transactions simultaneously with 3500 masternodes, unless you allow overlap. But that should be avoided, because it can happen that a masternode has the power to decide which of the 2 transactions he confirms during a double spend attack.


In other news: my buy orders are filled and I now own 200 DASH When I get more confidence in the technology, I'll probably look for buying at least 800 more, so I can participate in the second tier. I also added a donation address to my profile