Though for some things, the flavor of the lemon or lime goes well in a dish, along with the sour aspect, if you don't want that, you can use citric acid - a.k.a. sour salt. I keep a small container of that where I keep some salt, pepper, and a few other frequently used seasonings, so I can get to them quickly. 1 tb lemon juice is approximately equal to 1/4 tsp citric acid; some more, some less sour, and lime juice is a little less sour - approximately 4 tsp to 1/4 tsp citric acid. Just a pinch of CA can be substituted for a tsp of one of the juices, unless it is something where the flavor will be noticed. Most of the time it is for the sour. And how many people have ended up wasting the rest of lemons or limes, after just using a small bit of one?
It's also used when canning - adding some to some tomatoes, in case they are the low acid type.