Just my measly 2 cents worth here, but if your broker is telling you Humboldt is the reason your rates are going up, find another broker RIGHT NOW because the SOB is lying to you.
This year I renewed in place with a ~120% loss ratio. How did I manage that?
1) I have an excellent broker. She is one of the very, very best.
2) I concentrate on a long term relationship with my insurance company. We ride the dragon together, and you can't negotiate with them if you can't say "remember when?".
3) I am a very active participant in my renewal process. I am acutely aware of my short, mid, and long term loss ratio.
As for carrying excess insurance, unless your company is setup to immediately divest itself of every asset and provide absolute, unassailable protection for the principals in the event of a catastrophic accident, then you need insurance in excess of your policy. Keep in mind that the insurance you buy in Canada is in Canadian dollars and the exchange rate comes off your limit, not in addition to, in case of a claim in the U.S.