Brachot 16 - Workers and Bridegroom Say Shema
The workers may recite the Shema on top of the tree or on top of the wall of stones. If they started their work before the time to recite the morning Shema arrived, they are not required to descend, but can concentrate while saying the first phrase, and continue with the rest, where such extreme concentration is not required. However, they are not allowed do this with the Amidah (Standing prayer), since it requires long concentration, and they might be afraid to fall.
A groom is exempt from saying the Shema from the first night after his marriage (which was usually performed on Wednesday), and until after Shabbat - if he was not yet intimate with her. All this time he is too nervous to concentrate on saying the Shema, but after Shabbat he will be more at ease with his wife, and will be able to concentrate.
Rabban Gamliel married a woman, and nevertheless read the Shema the night after the wedding. His students asked, "Our teacher, you taught us that a groom is not obligated to say the Shema!?" He answered them, "I will not listen to you to stop myself from accepting the sovereignty of Heaven even for a moment." Rabban Gamliel knew about himself that he can concentrate in Shema, and he was teaching them the law that in that case one is a allowed to pray.
Antonius Heusler - Portrait of a Bridegroom