When I zero I normally have a cardboard box in the back of the vehicle.... I then just put 1" or 2" square of sticky silver duct foil, thats available on rolls in the centre, I leave these in the vehicle... I then put the box at 30-40 yds, take a shot, use the one shot zero function then move to the target centre, take another shot to verify, when it's somewhere close I then move it out to 100 yds for my centrefires and repeat to verify.
When doing this, place a small 2" object under the front of the box to tilt it up slighty towards the sky, the tin foil will show a lot more vividly this way...
Also if checking zero at further ranges just used heat pads you can buy a pair from the likes of home bargains, B&M, etc for a ÂŁ1, the heel versions have a sticky backing, so you can put them on whatever...these emit a lot of heat if you cannot see the heat signature clearly with other methods...
If I'm out with the airgun or rimfire, I basically use the box and tin foil initially then after that, if I want to check zero when out, just shoot at a piece of wood, fenceline, tree stump, etc then aim at the impact point again, then use your freeze screen/ one shot zero to move to correct POI...... this method is very very quick and you can check/verify in less than a minute.....