The best way to improve your squad's ability to defend the second base steal is to practice game situations or game-like situations without actual runners.
Most coaches don't stress working with their catchers and therefore they lack in good form. This drill will help with runners stealing second base, and give you a decisive advantage over your opponent.
Setting Up the Drill
You want to make it seem like an actual game as much as possible.
The pitcher stands in the circle with a bucket of balls. The catcher is to be behind home plate in full equipment in the crouch position. (This should be with thighs parallel to the ground, a fairly wide stance for balance, and their left foot slightly in front of the right, (for right handed players).
Draw a straight line across the ground in line with the left foot.) The catcher should extend their left hand (glove hand) out and make a fist with the thumb tucked inside. The right hand should be placed behind the glove pocket. This will enable better control and a faster throw to second.
Sharpening the Skills
Have the pitcher pitch a regular fastball down the middle of the plate. The catcher is to lean forward slightly to get to the ball faster.
As the catcher is catching the ball they should turn their feet so their right foot is perpendicular to the position that the left foot was in. They should not have taken any steps toward the pitcher except the shuffle turn. (Their left foot should be open to second base, which will allow the throwing arm to be in a straight line with second base.)
With the upper half of their body, they should be in a sitting position with their back straight (like a wall sit.) The ball is pulled with both hands up to the right of their face by their ear. The left arm should then separate with the right and point to second base.
With the ball in the right and an extended right arm parallel to the ground, bend it to a 90-degree angle, hand toward sky. Rotate the right wrist backwards (as if to show the python muscle.)
Grip and Release
With each throw, the catcher should have the same grip on the ball. I use the grip with my index, middle, and ring fingers crossing the seams. Keeping the "L" shape in their arm, follow through the throwing motion keeping in line with second base.
Their weight should shift with the throw. (Make sure not to shift the weight too soon, as this will create less speed on the ball.) The left arm should release and fall as the right arm throws the ball.
Importance of the Follow-Through
Your follow-through should force your right foot into the fielder's position. The ball should be going on a down angle to second base, not a straight line.
This will better enable the shortstop or second baseman to put the tag on. (The receiver's glove should start on the ground and be pulled up for bad hops, not started in the air as is often taught.) The catcher should not be stepping on the plate or any where near the plate.
Variations of the Drill
After this is done repeatedly (and don't worry it is not to be learned in one day!), try other pitches. For a ball on the glove side, the ball should be pulled across the body with both hands and into the throwing position. The body should not go to where the ball is.
This is the correct form as taught in Major League Baseball. My coach was a catcher in the majors and has a ton of knowledge. Best of luck to everyone!