Golf Instruction has been plagued with a “linear slide” philosophy for the last few decades. Rotational teachings haven't become mainstream yet, which is a very concerning issue since Rotational movement improves multiple areas of the golf swing. Lack of rotation puts too much emphasis on an arm pull-down dominated swing.
Slowing the arms down and keeping them on the trail side of the body is imperative for ingraining rotational movement, moving dynamic loft forward, keeping the path and face closer together, improving ball compression, solid ball contact and giving you more distance.
For a lasting solution to fix a slice, use this drill to work on emulating a proper body motion that will promote a swing path that is more right of the target. Starting with a closed club face, swing back and close the face at impact with an In to Out path. When this drill is executed properly the dreaded slice will be forever gone and a permanent fix will be ingrained.