In this work, we present a novel technique for in-vivo proton therapy range verification, and share the results of multiple experiments to determine its feasibility. This technique makes use of a hadron tumour marker (HTM), implanted at a short distance from the clinical treatment volume. Signals emitted from the marker during treatment can provide a direct measurement of the proton beam energy at the marker's position. The method was initially investigated through a Monte Carlo simulation, followed by two experiments at TRIUMF, in which candidate markers were activated with a variety of proton energies. Finally, the method was extended to heavy-ion therapy in an experiment using a 16O beam. In all these investigations, the range uncertainty obtained using the HTM was consistently on a sub-milimeter scale. Range uncertainty in proton and heavy ion therapy limits the prescribed treatment plan for cancer patients with large safety margins and constrains the direction of the beam in relation to any organ at risk. An easy to implement range-verification technique which can be utilized during clinical treatment would allow treatment plans to take full advantage of the sharp fall-off of the Bragg peak without the risk of depositing excessive dose into healthy tissue. This will lead to a better clinical outcome of cancer patients undergoing hadron therapy