Dual-sided vs. 360; securing rope

1. This is doubled-sided: https://centurionmagnetics.com/collections/dual-series

This is magnetic on the top and bottom faces of the magnet, but what about the side where it is red? Is that magnetic?

1. Here is a 360 magnet: https://centurionmagnetics.com/products/3800-omega-series

Is this magnetic only around the side or around the side AND the top and bottom faces?

1. You have the magnet on one end of the rope. If you throw the magnet into a river off a bridge that's pretty high, wouldn't the weight of the magnet pull the entire length of the rope down into the river? If so, you'd be screwed. How do you prevent this? Is it common practice to tie the other end of the rope down to something? If so, what do you tie that end to?