How can a country with a small land area conduct nuclear missile experiments?

You can do it in the Pacific Ocean. For example, 1946, the atomic bomb test conducted by the United States in the waters off Bikini Island; Hydrogen bomb test in1954; Most of the French nuclear tests were conducted on the coral reefs of Mururoa and Fangjiatao in the South Pacific. Israel and South Africa cooperated in conducting nuclear tests near South Africa and Antarctica. So if you want to do it, it's not a problem. The question is whether you dare to do it.