1.I can still remember the pride I used to feel at taking him onto Putney Heath and Wimbledon Common on the Number 74 bus.
at可用about来代替吗？为什么用onto？翻译本句。

2.We liked the idea of giving a home to an animal that had had a raw deal, so off we trundled to the RSPCA and saw this rather sweet dog.
解释so off，这个off的位置太奇怪了。翻译本句。

第一句的at因该是不能换为about的，at在这个地方有when的意思，onto应该是强调带狗 “到那儿去”，比较准确的表述，而且有点掉书袋的味道（当代英语中较少使用）。
第二句的off并不奇怪，本该在trundled后面，有away的意思，so当然就是表结果，off提前表强调。传统诗歌里常见。“off we go”之类。
翻译就免了，我最讨厌，还要去仔细推敲，自己做吧。
附上the commons的介绍
The Commons are an area of calm and tranquility in the midst of the urban sprawls of Wimbledon, Putney and Kingston-upon-Thames in South West London. The Commons comprise about 460 hectares (1,140 acres) of countryside split between Wimbledon Common, Putney Heath and Putney Lower Common. Putney Lower Common is separated from the rest of the Common by about 1.5 miles. Approximately 360 hectares (900 acres) of the Commons are a Site of Special Scientific Interest (SSSI) and Special Area of Conservation (SAC).