With my newer site I've built I am optimizing the page for a 4k search term. However, I found a few other kw's that fit appropriately into the article for writing purposes. So if main keyword was: "how to kill your dog", the secondary keywords are like "best dog killing stabbing methods", "what if the dog bites back", "how to start killing your dog". These keywords aren't just variations of the main keyword but rather related secondary keywords themselves each getting 200-500 searches. I stuck them into my article as three H2 headers. Density of main keyword is at 0.6% and these secondary keywords are used 1-2x each in article. I am just wondering if there is any issues or some kind of maximum amount of secondary keywords you can use in an article? I obviously only care about ranking for the main keyword and am just adding them as a bonus. Disclaimer: No dogs were harmed in the making of this post and all references or situations regarding dogs were purely fictional.