Nice looking job. Did you opt for a backer? There is plenty of range between nickle silver alloy melting point (you can figure well over 1600 F) and the lower temperature silver braze alloys (around 1200 F). Considering that the guard "should" have low strength requirements, 95/5 solder (95% tin 5% antimony)at around 14,000 psi tensil "should" be OK. If it breaks again, resolder with a steel backer.