If you shoot in conditions that can result in dings to your rifle scope (e.g., PRS or NRL matches), you should consider wrapping the scope using Camo Form by Gear Aid.
Camo Form is essentially a glorified Latex wrap bandage (albeit thicker) dyed in a variety of camouflage patterns. Camo Form doesn’t leave any adhesive residue when removed and will work great on something like a rifle scope which is hard to wash off.
I have used gaffer tape very often but realized it leaves residue if left on for too long and I have had to clean up quite a few items that I removed gaffer tape from.
If you need something that is non-adhesive but should provide basic scratch protection and will also help to camouflage black finish scopes, check out Gear Aid Camo Form.
A roll of Camo Form runs for about $16 or $17 depending on the retailer and can be had in a variety of Kryptek and Realtree patterns as well as MARPAT style digital camouflage and Mulitcam.