Yeah, it's an IDFK to the opposite team from where the ball was located at the time of the incident. However, what I really think you should think about is how quickly you decided to stop play in order to issue the sending-off/caution. If you had yet to make up your mind when you blew the whistle on whether or not you wanted to give a red card or a yellow card, it might have been too quick to stop play. When issuing a caution for dissent, it is often better advised to carry on with play and issue the caution at a natural stoppage in play. However, if you are going to send the player off, it is best to do so immediately. While you are completely justified in law to stop play to caution a player, you may raise some ire from the players and fans for doing so. Long story short, do you think you stopped play too quickly before you had decided whether or not to caution or send the player off?