@Roryhas granted me the shoe in to think ‘outside the box’
The key thing is of course to have a safe environment, not break the law (proximity to footpaths and roads) and not annoy neighbours
If you want a fairly simple target then setup some simple targets to hit, add something ‘reactive’ such as metal that will pint (as per Rory’s can lid) or a soft thing such as paper that will show your hits
A novel option (which can work for airguns but may not work properly for airsoft) is to put paintballs on golf tees
For an airgun a good centre hit will burst the paintball, a glancing blow or whizz past might knock or blow it off
For airsoft I suspect a BB at any decent range may just knock down a paintball unless you had a good fresh tournament grade paintball
But that does give a small target to try out your accuracy & your RIFs consistency
If you’re a student or road worker then put some cones out
However - be aware that hits will bounce away in various directions, so limited in where it would be suitable for garden targets
Cones are great for an easily relocatable but solid target of varying size (not just that cones come in all sizes but you can aim for an easy shot at the lower wider bottom of the cone and work up to the slimmer top of the cone. You can also pop a can on top or a stick through the cone holding up another target
If you have a few cones then space them around at various distances and practice switching target
Remember again that if you’re switching target then your hard backstop needs to cover the wider range of potential misses