In this situation banking the 7 would only collide with the 8 ball.  So the safety play is to thin the seven ball slightly with top left english and watch it roll behind the nine ball leaving the seven ball almost in its same location.  The advantage to this choice is hiding behind the 9 ball is a high percentage play. I can be to slow or fast by a foot and still be hiding.  Trying to hide in this case behind the 8 ball only gives me a 3 inch safe zone to go for while hiding behind the 9 ball gives me a foot or so due to the angle. Thin hitting the 7 ball is the key as you do not want to hit it to hard and leave it off the safe line you have established.  This would be hard to do since the 8 is also acting as insurance for your good safety in this case. Had you hit the 7 too thick you may still get away with this high percentage safety. 

You can see the end result below.

Now you have left your opponent with a much more challenging kick shot to save his game.  Placing the odds in your favor of winning the game.  You wont get ball in hand very often with this safety but your sure to get back at the table with a better shot than you started with.

Now if the above safety was not good enough to get ball in hand on your opponent then just try this one below. Its more aggressive. More margin for error but the results are a safety that is much harder to hit for your opponent.

Freezing the cue ball on that nine ball is almost guaranteed ball in hand for you. Come close and your opponent will have a much harder time dealing with this one.

The result is obvious

The end result is obviously a much stronger safety. A little more speed was added to the shot and a little left (outside english) which kept the cue ball on this line.