Green’s Dictionary of Slang

rocky n.

1. (UK drugs) a variety of hashish; also attrib.

[UK]N. Barlay Curvy Lovebox 45: What was you after? Es an’ some rocky hash.
[UK]J. Baker Chinese Girl (2001) 10: Some Rizlas, and a tiny piece of Rocky wrapped in silver foil.
[UK]K. Sampson Killing Pool 9: Quarter of Rocky on him, personal use, whatever.

2. (UK juv.) the erect penis [it is ‘rock-hard’].

OnLine Dict. of Playground Sl. [Internet] rocky n. an erection.

3. (UK juv.) a scavenger.

OnLine Dict. of Playground Sl. [Internet] rocky n. [...] one who removes things from wastepaper baskets/ rubbish bins, for personal gain. These would include apple cores, half-eaten sandwiches, biscuits (later eaten by the class spesh), pens, rulers – just about anything that still had some function to the Rocky.