Stealth Rock is your one and only way of effectively dealing with Ho-Oh, as with it, it can no longer come in on Arceus-Dark / Arceus-Ghost / Ferrothorn / anything else effectively, due to losing 50% of its health each turn. Stealth Rock setters must themselves not be Ho-Oh bait as otherwise Ho-Oh comes in on them easily, can weaken them with Sacred Fire, and then switch away, obtain its Regenerator and easily outlast your Stealth Rock user. Stone Edge Groudon or Primal Groudon, Stone Edge Landorus-Therian, Stone Edge / Toxic Gliscor, etc. I have used Stone Edge + Draco Meteor Dialga to lure in Ho-Oh before, as it often tries to come in on the turn Stealth Rock is set up, or on a Draco Meteor, at which point you can surprise it:

0- Atk Life Orb Dialga Stone Edge vs. 248 HP / 0 Def Ho-Oh: 432-510 (104 - 122.8%) -- guaranteed OHKO

Without Stealth Rock and enough offensive pressure to where Defogging is difficult, Ho-Oh will not be a problem. There is no way to fix the weakness that passive teammembers such as Ferrothorn and support Arceus have to Ho-Oh, with using Toxic on Ho-Oh as it switches in often being the best option. I'm going to offer a point of view, which is that there is no real counter to Ho-Oh, there are at most shaky checks, some of which are better than others. Sacred Fire burns + well-timed Earthquakes will ruin any "counter" you can offer. With a defensive team, if you are playing a competent player, you will lose to Ho-Oh unless you play perfectly, as the sheer existence of Ho-Oh is a problem for stall teams due to at least half the teammembers being OHKOed by it and giving it a free switchin as well. You are better off trying to read when Ho-Oh will come in on Ferrothorn / Scizor / whatever and doubling to your Arceus-Dark / Kyogre / etc.

To put it in one or two sentences, in order to deal with Ho-Oh adequately you need to build your teams so that its switchin opportunities are extremely limited, you need a sturdy and durable Stealth Rock user that is not Ho-Oh weak itself, and you need adequate methods of pressuring Defog so that you can either make the opponent pay a high price for their Defog turn or at the very least outlast their Defog user with your Stealth Rock user. Failing this, a way to lure Ho-Oh and KO it, such as Stone Edge from an Arceus forme that Ho-Oh can normally prey on, can be effective. It is possible to pivot into Ho-Oh with good predictions using resistances, but liberal use of Sacred Fire can compromise even this due to the burn chance, which is probably what makes Ho-Oh so overpowered, more so than Regenerator or 154 base Special Defense.​