An important aspect in the development of dependable software is to decide where to locate mechanisms for efficient error detection and recovery. We present a comparison between two methods for selecting locations for error detection mechanisms, in this case executable assertions (EA's), in black-box modular software. Our results show that by placing EA's based on error propagation analysis one may reduce the memory and execution time requirements as compared to experience- and heuristic-based placement while maintaining the obtained detection coverage. Further, we show the sensitivity of the EA-provided coverage estimation on the choice of the underlying error model. Subsequently, we extend the analysis framework such that error-model effects are also addressed and introduce measures for classifying signals according to their effect on system output when errors are present. The extended framework facilitates profiling of software systems from varied dependability perspectives and is also less susceptible to the effects of having different error models for estimating detection coverage.