I use dark chocolate and white chocolate chips for melting. They stay a little bit soft and have a texture I like, but because of their softness, need to stay in a cool environment. If you want harder bark, you'll need to temper your chocolate. This is a great step-by-step for doing that.
Cover a large cookie sheet in aluminum foil. Set aside.
Remove candy canes from wrapper and place in large plastic, ziptop bag. Using a mallet, bottom of a glass or rolling pin, mash the candy canes until they are in small chunks.
In a double boiler (or a small bowl over a pot of simmering water) melt semisweet chocolate chips. When completely smooth, pour onto cookie sheet and spread into a thin later (about ⅛"). Don't worry if chocolate doesn't spread to edge of cookie sheet. Place cookie sheet in freezer.
Using a clean double boiler, melt white chocolate chips until smooth. Mix in all but ⅓ cup of the candy cane pieces.
Remove cookie sheet from freezer, carefully spread white chocolate over the dark chocolate in a thin layer. Sprinkle ⅓ cup of reserved candy cane pieces on top. Place cookie sheet in freezer.
Once bark is completely cooled and hard. Remove from cookie sheet and break into large pieces.