The main ussue in hot cracking is to make sure your filler metal is not fully austenitic after being diluted with both kinds of base metal.  A common filler metal that is used for this is 309.  Also, make sure the weld beads are convex, not concave or flat.  The bead should also be around twice as wide as it is deep.  A bead that is as deep as it is wide has a tendency to hot crack.  As far as detection, hot cracks are usually pretty obvious to the naked eye, but if more stringent controll is required, use LPE.  Especially on the root pass.