Personal Umbrella coverage is needed to provide an extra layer of liability coverage above your other insurance policies. If you are liable for a large claim that exceeds the liability limits of your policy you can be held personally responsible and have a large claim against you and your assets. A Personal Umbrella policy will protect you from this exposure by going over and above your existing policies, just like an umbrella, and effectively increase the limits. You can provide an extra layer of protection from liability lawsuits by buying an Umbrella policy with limits ranging from $1 million to $20 million and higher.  This will blanket over all your assets whether that be your home, rental properties, boat, RV, Auto, Jet Ski’s, vacant land and so much more and kick in if and when you exhaust your limits on your policy and need that extra layer of protection. 
If there's one coverage to recommend it would be liability as we live in a litigious world so protect yourself and your assets as a lawsuit can wipe out all you've worked for.