Location, location, location! Once you dig a pond, you cannot 'move' it!
We'd like to put a pond in - but the prime location is near a maple tree....which is fine for 11mo out of the year, but that one month the tree looses all it's leaves would be deadly to a fish-stocked pond, unless it were fairly huge. Or a fairly huge net over it to catch the falling leaves and debris....cleaned daily....yeah, that's low on the priority list....
Ultimately, yes, any container can hold fish. Like stated above, one has to take into consideration: site, plantings (nearby and blown in), what planting zone (i.e. freeze point), quantity of fish desired, ability of local wildlife visiting pond (and preventing them from being harmed by it), cost considerations, electrical considerations (pumps run on electricity) - oh so much more!
Go to your local library - they'll have books on 'diy pond projects'. Heck, google it! There's much to think about, much to plan for, much to figure out.
Our 'pond' at present is a 40 gal hard plastic formed circle off the driveway - it's not deep enough to keep fish overwinter, so they all move indoors for the coldest season (5+mo of year). It's a complete pain in the rear to drain it every fall to reclaim whatever fish the bullfrogs haven't eaten, cover it with a piece of form-fitting plywood so it'll hold the snow load we place on it without cracking, and wait until spring to start it all again.
However, listening to the bullfrog on a hot summer night makes the effort worthwhile! Oh, and we never buy frogs...they come to us...and eat our 'feeder goldfish'. Annual expenditure of $3.00 worth of itty-bitty feeder goldfish early May....and we usually don't have anyone for the winter - except the frogs! Then the expenditures go up - buying crickets all winter to feed same said frogs....
Never dull on a homestead!