Seriously, even gaara can handle itachi, he simply stays in his sand and uses a third eye: tsukyomi countered
he blocked sasuke amaterasu itachi's would pose no problem and would easily be blocked
therefore susanoo is left, since itachi susanoo has no legs or lower part gaara can use the sand...
Just a short note : since kamui is a s/t technique and deals with dimensions , if a person is caught,for instance naruto and fukasaku couldnt they both use the reverse summoning, and summon themselves back to the mountain,
thoughts ?
Just an example