I have been using a system based on trials for the last 20 odd years and i am showing a profit.
It is very simple and involves a database of horses that have won trials in 2.4 or better at official Victorian trials as published in National trot guide. I also receive results direct from some clubs.
To paraphrase it all i do is give the horses that qualify 3 starts or 1 month to win or they are dropped from my data base my staking is just $1 each way.