In the context of intraspecific competition, the distribution of key resources within a territory could influence the spatial patterns of scent deposition by territory owners, in order to maximise the defensibility of resources and reduce the costs of their defence. We investigated the pattern of spraint deposition by the Eurasian otter (Lutra lutra) in Mediterranean rivers of southern Italy, testing the hypothesis that spraints are concentrated around deep pools bordered by riparian vegetation because these represent important patchy sources of food. Otters strongly selected pools throughout the year, marking the largest ones which probably supported the highest fish biomass. Sprainting sites at pools were also marked more consistently than sites elsewhere on watercourses. A positive correlation between the percentage of spraints next to pools (pool markings) and overall volume of the main prey in otter diet confirmed the importance of pools as sources of prey. These results are consistent with the idea that territory owners should concentrate scent marks on key resources, as an adaptation to the constraints of defending long and narrow territories, which follow the shape of the rivers. Pool marking increased in the warm season and in December–January, but was not correlated with monthly consumption of the main prey, raising the hypothesis of an additional, reproductive function of scent marking. In the absence of specific data on reproduction or births in our study area, this hypothesis needs further investigation.