Originally Posted by
beeftech
Your problem seems to be mostly related to the fact that you have a (full coverage bolt on) fender, and do not know how to properly set your chain tension by hand.
It shouldn't take you any longer to take your wheel off than that of a geared bike. The only thing slowing you down is your fender (and maybe a few seconds from un-doing the axel bolts).
Also, it's safe to ditch the chain tensioner, worthless gimicks.
EDIT: everything peabody said too.
Not precisely true, they're useful when you have axle nuts with worn out serrations and chain tension won't hold. Perhaps also when newcomers are learning what tension is good and what is too much, setting a tensioner is a lot easier than fidgeting with the wheel and nuts. Aside from that, if you need a tensioner to get proper tension, you're probably trying to set it too tight.