This is a general issue with speech recognition, unfortunately. Rejecto is designed to reject phonemes other than the keyword which surround the keyword and utterances that are evidently not utterances of the keyword. But a one-syllable word which rhymes with a one-syllable keyword in a language model that only contains very few one-syllable keywords is very unlikely to be recognized as a different word because there is very little information in the model which would allow evaluating whether it is the one word or another. It has a very high probability of being recognized as a less-probable version of the same word.
To me, it doesn’t sound a highly-likely usage scenario since your app is probably more designed for users to say “meow” to it than to intentionally interact with it by saying “peow” with the expectation that “peow” isn’t recognized. But probably the most effective way you have available to prevent recognition of “peow” is to add “peow” to your main language model and then ignore it when it is recognized. Does that make sense?