A liquid dispensing instrument, such as a marker assembly, the instrument having a barrel, a release mechanism, and a cap. The release mechanism can comprise a deformable arm affixed to the barrel or the cap, for pushing the cap and barrel apart. In one embodiment, a liquid dispensing instrument comprises a barrel having a first end and a second end, and a cap disposed over the first end of the barrel. The barrel has a deformable arm having a fixed end affixed to the barrel and a free end, the deformable arm protruding radially away from the barrel. The free end of the deformable arm pushes the cap away from the first end of the barrel when the deformable arm is pushed radially toward the barrel.