What are the best ways of combating detonation?

Mapping a friends engine at the mo, but have had to remove alot of ignition advance to get rid of the detonation.

Down to about 13 deg @ 0.5 bar under load.

I think most of this is due to the poor chamber design he now has after fitting a decomp plate (no more squish).

I know that backing off the advance moves the ignition event back in the cycle and lowers the post ignition cylinder pressures which in turn prevents post ignition gases from igniting on their own after the spark.
I was just wondering if there are any other methods of reducing det that i could use?*

The ACTs are already pretty low and the engine also runs at a decent temp.

Would water injection give me any det protection other than cooling the charge?

I realise stu might not want to give away his secrets, so one for the home mappers really.

Any suggestions welcome.

Cheers,

DC.



* bar removing the plate and rebuilding with some dished pistons and/or careful enlarging of combustion chamber. Not my engine so can't open it up.