Smacking rhymes with:
attacking, backing, cracking, hacking, jacking, lacking, packing, racking, sacking, snacking, stacking, tacking, tracking, unpacking, whacking, wracking
Smacking sounds like:
samsung, samsung's, sansing, schmiesing, schmoozing, senescence, sensenig, sensing, sequencing, shenanigans, simkins, singing, sinking, smashing, smoking, smoking's, smoshing, smugness, snacking, snagging, snaking, sneaking, sneezing, snoozing, snugging, squeamishness, ssangyong, sunshine's, swensen's, swinging