For a cactus or succulent, the sign that you’ve over watered is that the base has turned mushy and brown. Now if the top is healthy and hard, well, it can be saved! In a case like this you would, quite literally, decapitate the cactus by cutting the healthy part of the cactus from the rotting, unhealthy part. You’ll need a very sharp knife and a pair of very thick gloves and then you cut until you don’t see any brown colouration inside the core of the cactus. Once you’ve cut the healthy section from the unhealthy core, you’d discard of the unhealthy part and wash your planter thoroughly with soapy water. You won’t repot the healthy top section anytime soon. It needs time to callous over so you must place it in a cool but dry area of your home for at least 7-10 days before reintroducing it into soil. When the fleshy part of the healthy cut has calloused, only then can you replant it into VERY gritty soil.