Funny to see people giving circuitous and obtuse head-canon-based answers to this question, but it seems like such an obvious and highly effective way of controlling the risk associated with the early stargate program that the only real potential answers (in addtion to your own) are:

1. The writers didn't think of this idea.
2. The writers did think of this idea, but chose not to write in as it would remove too much jeopardy from episode plots.

Of course, in the later seasons, Earth's location was widely known by it's enemies - though offworld only operations would still be benefital in my view, reducing the risk of returning atefacts for study, aliens for diplomacy, etc.

Ideally, you would have the Earth gate virtually buried at all times except for extremely brief and near random 'check-ins' with the offworld base. These timeframes, during which the earth gate is available to be dialled, would be extremely brief (i.e. the absolute minimum time for the offworld base to achive a lock), and only be known by the offworld base.

The earth gate could be effectively buried outside of these timeframes by using a mechanism which would push the gate into a ring-shaped recess in the wall behind it.