Word Puzzle Game - Add Extra No Occurrences

I have a simple Word Program here called PuzzleGame.java. It works perfectly but I wanted to add some bells and whistles to it. So I want to be able that if the user selects the same letter more than once a message comes up letting the user know that "That letter has already been selected, try another letter."

I am certain that if would go in the 'else' of the 'if( )' that I am providing.

import java.util.Scanner;
public class PuzzleGame {
public static void main(String[] args){
String secretPhrase = "BIG JAVA";
String guesses = " ";

[Code] .....

I am thinking maybe after the else in this if statement.

if(guesses.indexOf(secretLetter)== -1) {
System.out.print("-");
notDone = true;
} else {
//something here. I am not sure how to go about it.
System.out.print(secretLetter);
}