There are products like these out on the market. I'm just too cheap to buy one and pay for shipping. I spent about $1.88 total to do this project

You will need:

1 ea. Buckle type lg-med dog collar (I already had one)
1 ea. Large Carbiner(I bought mine from a gas station 2 for $1)
They were actually key chain holders
1 ea. Dual Swivel from the hardware store ($.88)

Step 1: Collect All the Necessary Items

Yes, this is common sense!

Step 2: Put It All Together.

Thread the Dog Collar through one end of the dual swivel. Clip the carbiner through the other.

Step 3: Attach the Dog Leashes

Using the carabiner, clip 2 dog leashes through the leash loops, or through the D-rings.

Step 4: Walk the Mutts

Slip your hand through the collar on the dual swivel, and adjust to fit your wrist. I hold the collar open, slip my hand in, and hold the collar like I would a flashlight. It leaves the other hand free for the pooper-scooper.

Enjoy your tangle free dog walks! This has shortened my walks because I don't have to stop and untwist the leashes every couple of minutes. I suggest using 4 foot leashes with this contraption. I have six foot leashes, and they seem a little long for me.

Told you this was too simple.