make yourself as unprofitable as possible.
don't leave large amounts of res sitting on your planet, invest them as soon as you can.
if you're saving up for something and going away to the comp, fill up your small cargoes with your res and send them on an attack mission to an inactive planet (or very low ranked player who will have no chance of fighting back) if you can find one on an attack mission, setting the speed as slow as you need, so the mission will last as long as as you are away frim the comp.
and build some defensive structures as well.
chances are you might not have to be fully concerned, because the top players just probe as many people as ppssible to find as many targets as possiblle. if you make yourself unprofitable to atttack, you may stilll be probed, but you wont have to worry about an attack.
yeah, i'm a cranky 'oul fucker. deal with it.