The answers to the following clues will have something in common.

1. Tough situation

2. An irregular coin*

3. NASA Martian explorer

4. A golden one was driven to complete the first transcontinental railroad

Answers:

 

1. SPOT

2. FIDO*

3. ROVER

4. SPIKE - - - Common dog names 

 

*A fido is a coin that is defective, having been incorrectly minted. It is often prized by collectors (numismatists).

 

Credit: 

Fred Piscop 

DOG DAZE