Have carried many years in ankle holster - but almost exclusively when wearing lace-up boots (approx 6"). While I understand that some people do it, cowboys boots a no-go for me with anything larger than a NAA min-mag. The laceup boots however, for me anyway, allow a good elastic holster (preferably 5") to be used without the "garter thingie". Downside is where the holster/barrel rides can cause the top of the lining on left boot to wear/tear much quicker than on right boot (opposite for southpaws).
Another key element - in my not so humble opionion

- is a small, especially lightweight gun. My numero uno favorite is S&W 340PD (with CT grip) that goes loaded at only 15 ounces. Second in line (and a separate holster for it) is Kahr PM-9 (19.4 ounces loaded). I've tried many other guns in ankle holsters and ones like the Glock 26 - for me anyway - get to feeling like a boat anchor with much physical activity. Another "almost requirement" is boot cut jeans and possibly an inch more length than normal. I carry one of the guns mentioned above so frequently in an ankle holster, that I can't remember the last time I bought pants of any kind without the carry method in mind.