[1.8] Best place for markBlockForUpdate

Hey folks,

I need data on client and server side synced everytime a player rightclicks the block.

I know that I need to use markBlockForUpdate and description packets. But when i call the markBlockForUpdate before opening the gui the data is not there when I need it.

So where should I call it?

@Override
public boolean onBlockActivated(World worldIn, BlockPos pos,
		IBlockState state, EntityPlayer playerIn, EnumFacing side,
		float hitX, float hitY, float hitZ) {

	if(worldIn.isRemote) return true;

	worldIn.markBlockForUpdate(pos);
	playerIn.openGui(ShadowsRising.INSTANCE, ShadowsRising.GENERATOR, worldIn, pos.getX(), pos.getY(), pos.getZ());




	return true;
}