In general, if you are sued as a result of an auto accident or HO liability situation, your primary policies will provide/pay for your defense. You don't need an umbrella/excess policy to pay for that.
Right your primary policy pays for defense but doesn't pay for a verdict that's more than your policy limits..that's where the umbrella policy would come into play. Also, if it's a large case and both your underlying and umbrella policy is going to come into play both typically provide a defense and work together.
Also you still want to be careful regarding reporting simple claims (i.e. 1 veh accident where there's no damage to your car) because every year when your policy comes up for renewal most companies will look at your claims history, driving history, etc before agreeing to renew you.