“Lord of D.” cannot negate effects; he only prevents Dragon-Type monsters from being selected as targets of effects. Once a target has been selected, the effect of “Lord of D.” is irrelevant.
If your opponent activates “Ring of Destruction” targeting your “Lord of D.” and you chain “D. Tribe” to change “Lord of D.” to Dragon-Type, “Ring of Destruction” will still resolve and destroy “Lord of D.” since he was selected as a target before he was changed into Dragon-Type. If your opponent activates “Ring of Destruction” targeting a Dragon-Type monster you control and you chain “Call of the Haunted” to Special Summon “Lord of D.” from your Graveyard, your Dragon-Type monster is still destroyed for the same reason.
If you have “Lord of D.” on the field, and activate “Premature Burial” to Special Summon a Dragon-Type monster from your Graveyard, that is okay, but if your opponent later destroys “Premature Burial” your Dragon-Type monster is also destroyed because “Premature Burial” is NOT selecting your Dragon-Type as a target.
While you have “Lord of D.” on the field you cannot equip your Dragon-Type monsters with Equip Spell Cards, but if you already have a Dragon-Type monster equipped with an Equip Spell Card when you Summon “Lord of D.”, the Equip Spell card is not destroyed or negated, because “Lord of D.” only prevents Dragon-Type monsters from being selected as a target.
“Lord of D.” will NOT stop “Dark Hole”, “Mirror Force”, “Raigeki”, “Fissure”, “Smashing Ground”, “Hammer Shot”, or “Amazoness Archers”, nor will he protect your Dragon-Type monsters from their effects, since these cards affect the whole field and do not select targets.