ok then consider structuring your sketch so its in standby mode until its woken by an interrupt
also, from an atmel appnote/tech sheet thingie:
"By default all peripherals will be connected to GCLK generator number zero (GCLKGEN[0]). As this generator is used to generate the main clock it will always be on in active mode as well as the idle modes. The clock from this generator will then be propagated further down the clock tree than necessary. This will cause higher power consumption.
In the power measurements that are presented in the datasheet all peripherals are connected to a GCLK generator that is not connected to a source oscillator. The only exception to this is the DFLL which has its reference clock connected to a 32kHz clock crystal. In the code distributed with this appnote code can be found in the function switch_gclkgen_to_peripherals(). Switching unused peripherals to a GCLK generator that is not setup with a source oscillator is something that will save power in all applications."