Roberto, you are absolutely correct, tisking 10% of the bank on any one race is absurd risk management.
The racingtowin website advises 10% if I understand correctly.
I apply 30% of the bank per day and then proportion that across the total number of races. In some races there may be more than one selection and therefore I proportion the stake according to the odds, a simple spreadsheet is available on their website, it is easy enough to construct though.
To illustrate using yesterday as an example, 7 races where recommendations were made:
Assume betting bank is £1000.
Total available to bet for the day = 300 (1000 x 30%)
Total available per race = 42 (300 / 7) In practice I would round this up to 50.
In a race where 1 horse is recommended the stake is logically 50. Where there are 2 or even 3 then the stake is proportioned according to the odds to give equal return if any of the 3 recommendations win. Clearly if non win the loss is 50.

Hope that helps. If you want the spreadsheet, email or IM.