He remained active and engaged even later in his life. Rapper Tauheed K. Epps, who records as "2 Chainz", sampled Lehrer's song The Old Dope Peddler [PDF] for his track Dope Peddler, asking permission to use a snippet. Lehrer wrote back:
As sole copyright owner of 'The Old Dope Peddler', I grant you motherfuckers permission to do this. Please give my regards to Mr. Chainz, or may I call him 2?
We linked to his lyrics, although they are slightly inconveniently PDF files, because in 2020, he placed all of his lyrics in the public domain. A couple of years later, he did the same with all his original melodies, ending the disclaimer on tomlehrersongs.com:
In short, I no longer retain any rights to any of my songs.
So help yourselves, and don't send me any money.
Legend.