The scar on the heel bulb is also a scar on the coronet. Because the coronet is scarred, there is a line in the hoof wall growing down from there. You do not need shoes or boots to protect it. You do need to keep the hoof well trimmed, as any excess hoof wall growth will put additional pressure on that area and it can develop into a wider crack. However, as soon as you trim the hoof again, that will take the pressure off and it can heal. As long as the hoof is properly trimmed and balanced you do not need to worry about this. The one thing that you can do, is to see if you can find a balm that will soften and heal scar tissue. This could be massaged into the coronet and heel bulb. If it works, then the hoof wall could grow in stronger, without the little nick in the coronet that is expressed in the line on the the hoof wall as it grows down. Unless you can heal the scar, that line will always be there, but it will not be a problem as long as you get a good trim on a regular (6 week) interval or whatever your Hoofcare practitioner recommends based on your horse’s rate of hoof wall growth.