Searching for evidence of ``cold'' nuclear fusion in deuterium-loaded Ti and Pd foils with plastic track detectors, we detected the emission of \ensuremath{\alpha} particles from trace-heavy-element decay, but found no evidence of dd fusion. Cycling ${\mathrm{TiD}}_{2}$ and ${\mathrm{PdD}}_{g0.4}$, in high-pressure ${\mathrm{D}}_{2}$ cells between 1 and 15 bars and 77 and 300 K, gave an upper bound of 0.7 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ for the mean rate of dd${\ensuremath{\rightarrow}}^{3}$He+n fusion. For electrolytically deuterated ${\mathrm{PdD}}_{0.8}$ our upper bound is 0.0018 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$ for the mean rate of dd\ensuremath{\rightarrow}p+t. This is \ensuremath{\sim}1.5\ifmmode\times\else\texttimes\fi{}${10}^{6}$ and 180 times lower than ``cold''-fusion rates reported by Fleischmann, Pons, and Hawkins and Jones et al., respectively.