Dropping your Line
After the player gets a long enough line to go past 300 miles, he/she will need to watch out for mines which appear on the sides of the screen periodically below 300 miles. These mines will blow the player's line up when going down or up and he/she will end up catching no fish. This can easily avoided by not getting close to the sides, but it does make it slightly harder to avoid catching fish and tapping to drill becomes more important. If you've purchased the Diamond Drill, you can cut through them.
Pulling the Line Back Up
The player must watch out for the mines on the side when he/she is going back up from below 300 miles. They will blow up the hook and player will lose all the fish caught. This actually can be a quick way to restart if you are going for any elusive fish (such as the very rare Othulhu or the rare Giant Squid) and do not get deep enough before catching a fish. You can't drill a mine if you're pulling the line back up.