Bike is a Fat bike - I run the gears 1x10
Kona Wo
when i bought bike - upgraded gears to 1x10
but never changed rear rim or free wheel. the 10 rear cogs just fit on the free wheel
so been riding heavily all winter in snow and cold since got bike in november
recently been having problems with the rear cogs going loose while riding, happens when i go to hardest gear and ride

not sure why it loosens
i been using my free wheel log nut and wrench to tighten, and yes i click it all the way, but still comes loose every so often?

so solutions to why this still happens. i do notice that the hardest cog so make it a little difficult to fit in the log nut a bit

suggestions?
is it possible to ride without that last gear? as in the small hardest gear ring? if so what would i put there to hold everything in place and be able to lock the nut all the way?

as i don't really need that hardest gear often
thanks all

I'd try lock-tite or a new lock ring (or replace the first cog) before I considered taking out the high gear... yes, you could remove a gear and replace with spacers but that should only be a last resort (spacer would have to be on the low gear end and you'd need a new 12t or 13t cog meant to be a first position cog... which kind of defeats the idea that you are proposing).

Are you torquing it properly ? My Shimano requires 40nm to lock it down correctly.

there may be a little un-noticeable play in the cassette, I'd take it back where you got the bike or upgrade done

or try a thin spacer before you slide in the cassette, torquing down further won't help if you are already contacting the hub body

Are all necessary spacers installed and the lock ring properly torqued? The cassette must overhang the freehub (not freewheel) body enough that the lock ring bottoms on the small cog NOT the body, and be sufficiently torqued. IIRC an 11-speed body needs a 1mm spacer behind the cassette for a 10 (9,8)-speed cassette to be clamped correctly.

I am not sure what a "free wheel log nut and wrench" is but you need the correct lock ring tool and preferably a torque wrench. The typical 40 N-m torque is more than most people realize.