Oliver Cowdery initially skipped the word own here in 𝓟 but soon inserted it supralinearly (there is no change in the level of ink flow). The Book of Mormon text often uses own when referring to one’s strength, especially when the verb is depend or boast:
In the case of Mormon 3:9, scribe 2 of 𝓟 originally wrote the text without the own, but then almost immediately he added it supralinearly. Similarly, in Mormon 4:8 the 1830 typesetter seems to have omitted the own. There is clearly a tendency to omit the own. For additional examples of omitting own in other prepositional phrases, see the list under Enos 1:10. Despite this evidence, sometimes there are instances in the earliest text where own is not used with strength when it could have been, as in these two examples:
In each instance, we therefore follow the evidence of the earliest textual sources. Here in Mosiah 10:11, the critical text will accept the reading “they depended upon their own strength” since the correction in 𝓟 appears to be virtually immediate.
Summary: Maintain in Mosiah 10:11 the corrected reading in 𝓟: “they depended upon their own strength”.