I think he dont just split his chakra, he also split his soul like voldrmor in hp.
I mean the arms of his soul was sealed and then he make it to use they again, hes a genuis and have knowlege of near everything.
His chakra is in all the curse seal he implanted on his victims. Therefore in order to completely seal or get rid of orochimaru, you have to hunt down and seal/kill all the people with the curse seal and there are loads. Sasuke after killing orochimaru, went to the hideout and released a whole host of them into the wild.
Its near impossible to track them all down and seal/kill them therefore orochimaru is always capable of coming back, through this means
You may watch the Konoha Arc Invasion Orohimaru vs 3rd Hokage, short explanation he has seal himself to all the Cursed marked he has given (Sasuke - Gone) (Anko - Gone) (Kimimaro - Seal back by Edo Tensei) and (Mizuki Sensie, currently in jail Seal intact)